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Fitbit One vs Fitbit Flex: Which is Better? (An Experiment)


I’ve been on a Fitbit kick for a few months now, and have spent quite a bit of time getting to know the Fitbit One, which I really love. After I lost my second one, however, I started to think that maybe I should get a Fitbit Flex instead, since they’re harder to lose, being strapped to your wrist.

Why Fitbit?

I don’t want to spend too much time discussing the merits and flaws in the various personal health trackers. I had a Jawbone Up and hated it. To be fair, I got one of the early ones, before they issued the refund for anyone who wasn’t happy. For those who are curious, the manual jacking-in to sync and the cap for the jack that always ended up lost were the main reasons the Up was a massive letdown for me, and why I like the Fitbit so much more.

I also have the Aria scale (love it), which lets me weigh myself and automatically logs it to my Fitbit dashboard, so I don’t have to face the shame of manually entering it. And I’m not a runner, so the Fuel band didn’t make much sense. I’m super-excited to learn more about the Amiigo, but I really hope it works with the Fitbit API so I don’t have to lose the single-dashboard awesomeness with the Aria and everything else.

The Fitbit’s developer API platform is a big reason I went with them. They integrate well with lots of other apps and services, and that’s pretty cool. This one in particular seems rad.

So first the basic difference:

Features both the Fitbit One and the Fitbit Flex have:

  1. Pedometer – although the One is meant to be worn on the torso, the Flex is a wristband
  2. Sleep tracker
  3. Silent alarm
  4. Access to the Fitbit dashboard which allows you to log food, water, other exercises, friend rankings, etc.
  5. Bluetooth syncing with iOS app and also to your computer with a USB wireless dongle

Features the One has over the Flex:

  1. LED display that shows step count, calories burned, etc
  2. Altimeter, to automatically track stairs climbed

Features the Flex has over the One:

  1. Lives on your wrist – put it on and forget about it
  2. Arguably does a better job calculating non-walking, arm-related activities like swimming
  3. Persistent connection link with your iPhone, so you get a real-time step counter display, versus periodic syncing with the One

My Hypothesis

The Flex measures steps by the swing of your arm, not the movement of your torso. This seemed like it could be a problem for me for a few reasons. First, I don’t always swing my arm while I’m walking (if I’m carrying something, walking the dog, etc.) — and second, I’m Italian and talk with my hands all the time. No, I mean All. The. Time.

I was afraid the hand-talking would over-inflate my numbers by counting non-step, hand-wavy business, and that I wouldn’t get credit for legitimate steps I did take if I was using a handrail or for whatever reason wasn’t swinging my arm. (Spoiler: you don’t.)

I expected the Flex to show inflated numbers overall, since I move my hands a lot.

I should mention, I’m already starting this with the notion that the One is probably more accurate, simply because of how it calculates steps, and because short of physically, manually calculating every actual step throughout my day, I have to assume one of the two of them is “more right”. My goal here was to determine how big of a difference there is and whether specific activities are more prone to erroneous step-counts than the other. Having used the One for a few months, I am very comfortable with its overall accuracy.

The Test

Naturally, I decided to test it out. I’m currently wearing both the Fitbit One and the Fitbit Flex at the same time, and have put together a spreadsheet of my findings, which I’ve been logging at various times during the day. I will continue this experiment for a week, updating this post (and the spreadsheet) with new data points.

A few points of interest: I am wearing the Flex on my right (dominant) hand, and have it listed in the dashboard as being on my dominant hand. I wear the Fitbit One clipped to my bra, between my boobs, which is one of the recommended placements for it. (Insert TitBit joke here.)

The Flex does not seem to erroneously register typing as a step, which I’m glad for. I type very aggressively, so that would have been an instant deal-breaker for me.

Also, the graphs below were captured using data from a Tuesday, which is my work-from-home day, which is why the step level is much lower than other days you’ll see in the spreadsheet over time. My step-count is always very low on Tuesdays.

Here’s the raw data so far from the spreadsheet:

And here’s a breakdown of the data represented in each column:

  1. Date: date of entry where both the One and Flex were synced at the same time
  2. One: step count from the One
  3. Flex: step count from the Flex
  4. Delta: difference between the current step count of both (One – Flex)
  5. One Variance: difference between the current step count of the One, and the step count for the One from the last log entry
  6. Flex Variance: difference between the current step count of the Flex, and the step count for the Flex from the last log entry
  7. Variance Delta: difference between the One Variance and the Flex Variance (One Variance – Flex Variance)
  8. Notes: contextual notes on the activity performed

While the Delta is interesting by itself, the Variance Delta is potentially more interesting to me, since it will help me understand which activities tend to register with particular wide gaps in step counts. You’ll see the Variance Delta in the block immediately after “Dinner+drinks” is the highest so far, and dinner and drinks is a period of almost no walking, but lots of hand-wavy, enthusiastic talking.

As you can see, overall, the Fitbit dashboard graphs look pretty similar:

Fitbit One
Fitbit One
Fitbit Flex
Fitbit Flex

What’s more curious is that the Flex seems to think I had 34 Very Active Minutes, which I can sadly assure you I did not. The One thought I had 3 Very Active Minutes, which is closer but frankly, still might be pushing it. (I told you, I worked from home. Don’t judge me.)

Fitbit One
Fitbit One
Fitbit Flex
Fitbit Flex

Breaking it down, it looks like this so far (taken from the spreadsheet):

Screen Shot 2013-07-17 at 12.18.47 AM

Screen Shot 2013-07-17 at 12.18.35 AM

I will continue to log my data, and annotate any particularly unusual activities for context.

Keep checking the spreadsheet, and check back here in a week or so for my conclusions. Leave your questions or thoughts in the comments, or ping me on Twitter @snipeyhead.

[box type=”note”]UPDATE: I have been logging from 7/15 to 8/5, and so far the difference in steps totals almost 50k. The Fitbit Flex has logged 47,784 more steps than the One, which I believe supports my theory that the Flex over-attributes steps. I will keep logging for the rest of the month, and we’ll see where it shakes out. You can view the raw data and updated charts here.[/box]

About the author


I’m a tech geek/dev/infosec-nerd/scuba diver/blacksmith/sword-fighter/crime fighter/ENTP/warcrafter/activist. I run Grokability, Inc, and run several open source projects, including Snipe-IT Asset Management. Tweet at me @snipeyhead or read more...

  • Jean-Pierre

    Great article!

    It would be a good idea to add one concurrent product in your test. I have the feeling that my amount of steps was much higher with my lost Fitbit One in comparaison with my new Withings Pulse.

    • Hi Jean-Pierre – I’m not sure what you mean by adding a concurrent product. Are you suggesting adding a third personal tracker? (If any companies out there want to send me one, I’m happy to incorporate it!) 😀

      • Jean-Pierre

        Yes, I would like to compare Fitbit One to Withings Pulse for example. The Pulse for example minimizes my steps count.

        • They’re welcome to send me one and I’d add it to the test 😉

  • datavortex

    Excellent, very useful. Thanks.

  • ruggergrl

    Thanks for the information. It is very helpful!

  • penlynwilson

    Thanks for this post. I lost my One this morning and was considering a Flex. Think I’ll stick with the one.

  • Bridget

    I’m curious about why you are wearing it on your dominant hand since the recommendation is non-dominant. Do you think that skewed your results?

    • I’m wearing but on my dominant hand because it’s the hand I prefer. I know that sounds like a pat answer, but I wear bracelets and such on my other hand. That said, I started wearing it on non-dominant hand at the beginning of this week and will let it run as long as the first test. I already suspect funny business because when I walk, I usually keep my non-dom hand in my pocket, so it won’t register steps. I think I personally am just not a good candidate for wrist-based trackers. But we’ll see how it goes. I’ll update here as I go.

  • Keith

    I’m currently using a standard pedometer and thinking of switching to either Fitbit One or Fitbit Zip. I ride my bicycle every day and my standard pedometer records my bicycle rides as steps and calculates calories burned accordingly. As far as you can tell, would that also be true of the Fitbit products?

    • Honestly, I’m not sure, since I don’t do much biking. (I live in NYC, and the cabbies stress me out too much for that to be a thing I do for fun.) I know on my desk cycle, if I put the fitbit on my shoe, it does record cycles as steps, but I doubt it would do so if you wore the One on your torso.

      • velogiraptor

        Has the hand-in-the-pocket thing actually had an impact on your flex’s count? I walk to and from my car (1.6 miles round trip) mostly with my hands in coat pockets. This could be the single deciding factor for me vs. the One.

        • Yeah, it actually had a pretty big impact. I found myself having to remember to take my hand out of my pocket, but I’d often forget. It doesn’t register the step when your hand is in your pocket. 🙁

  • asreyes8022

    I absolutely love that you posted this comparison test. I am big on stats and graphs to back up observations. I still am not sure which one to get, however. What is your feeling on each one during sleep. Is the One more cumbersome at night with the wrist strap?

    • I do feel like the wrist strap for the One isn’t that well designed. It’s not cumbersome or anything, but the device did fall out one night (one night out of many where it didn’t), causing me to panic and search for it in the morning. I do feel they could have done a better job with it, in making sure it’s secure in there, but it wasn’t particularly cumbersome. It *is* something that you have to remember to put on and activate sleep mode on, versus the Flex, where you just need to tell it you’re sleeping (which I often forget to do.)
      I’ll try to do a better job of telling it I’m asleep, and then see if the numbers are different for sleep patterns in flex vs one. Will post results here when I’ve got some data to report.

  • Mr. Bill

    Thanx for the great analysis. Love the dinner + drinks variance example. Happens too me all the time & I don’t drink 😉 I think I’ll go out & get the One. My son is using it as a company experiment with their employees & it is a huge success.

    • Thanks so much for the kind words!

  • Nikki Anderson

    could you wear the flex on an ankle? if it would fit that may help with accuracy as hand talking could not be counted as steps as well as not swinging your arms while walking. I found this because i’m torn on whether to order the flex or one. the only reason i’m considering the one is because it counts stairs & the flex does not. otherwise the flex sounds a whole lot more convenient.

    • My ankles are too big for me to wear the Flex there, and I’d also worry that my general leg-fidgety-ness would confuse it, but I guess it depends on your ankles? The shape of the Flex wristband also seems like it could be weird around your ankle – the “top” side of it is pretty flat, meant to be worn on the flat-ish part of the wrist. I honestly don’t know though. I wish Fitbit would make some more options for the Flex/One holders besides different colored wristbands.

      • Nikki Anderson

        Thank you for your reply. This is really helpful. I tend to retain a ridiculous amount of water in my ankles so there’s no way it would work for me. I wasn’t sure how roomy they went though. I think I’m going to go with the one after all. Thank you so much for your help.

        • You’re very welcome! Let me know how the One works out for you! Protip: Wear it clipped into your bra either on the strap or between your breasts on the material that connects the cups. I lost one with it clipped to my pocket (I had it on the outside, not the inside, so my fault), but it’s harder to lose if you wear it on your bra, and it’s small enough that it can’t be seen outside of your clothes if you wear it in between the boobs. I’ve haven’t lost my current one yet, since I moved it there – and I am almost never without a bra, so it makes it pretty easy to remember to wear it.

  • B72

    great comparison and the data really helped.

    I’ve currently mislaid my one so am looking at a replacement and wasn’t sure if I’d be better with the flex, but this has pushed me straight back to the one. Shame its not possible to put on chain tho’!

    • Yeah – although I admit the first one I lost, I had clipped to my pocket the wrong way (clip inside, fob outside) and they recommend the inverse, which is definitely more secure.
      I can’t tell by your name if you’re male or female, but if female, I definitely suggest clipping it to your bra between your boobs. It’s been pretty solid there for months now. If male, you might just be stuck with the pocket setup. 🙁

  • Scott Marcus

    I’ve had the a couple of the FitBit “One” devices, though I think the first one had a different name — before they came up with “One”. They both died, after I forgot to take them out of my swim trunks and jumped in the pool.

    My wife just got me the Flex as a gift, so I’m going to try it out. I always have a pedometer (New Balance Via Slim: seems fairly accurate) with me in my pocket, so I can use that to compare the number of steps. Also, I have a Philips DirectLife activity monitor that I wear around my neck, and I can use that as a comparison as well.

    The nicest thing about the Philips device is that it is waterproof, so I don’t need to take it off to swim. It gives me some credit for swimming, but less than the actual calories that I’m burning, I believe.

  • Linda

    I’m trying to find out if the flex will track my swimming. I just bought it and am getting different responses when I look online. It seems you can manually log it, but I’m not sure how that works yet. Do you have any further info on that?

  • Joker

    I am a runner, and normally I try running on synthetic tracks, is the fitbit one the better option for me? the Body Media core is simply too expensive!. Please help.

    • Hi! As a runner, I think the One is a great fit for you. Since it lives on your torso, whether you use your arms on a treadmill or don’t, your steps will be counted. Plus, Fitbit integrates with running apps like runkeeper.

      • Joker

        Thanks, I have decided to go for the one. I’d like to get stats the fair way and earn my badges, ain’t exercising my arms 😛

        • Sounds good! Let me know how you like it!

  • ANI

    This is a fantastic comparison, thank you! However I’d be curious to see the result when wearing the One on your trousers or waistband, as I am a guy I don’t really have the option of clipping it to a bra.

    • Hi ANI! I didn’t see any difference between wearing it on my bra and when I wore it clipped to my jean pocket. I switched where I have it clipped just because it felt more secure clipped to my bra, but as long as you have the device-side in (not the clip side), which is how they recommend clipping it to your pocket, it should be pretty snug. Shouldn’t be any difference in numbers tho.

  • Scott Marcus

    I tried wearing it on my non-dominant hand (my right hand, as I am a lefty). The Flex seemed to under-report my steps by a wide margin, compared to my pedometer. The flex gave me credit for around 16000 steps, while my pedometer had me at around 25000 (sorry, I didn’t record the actual numbers). So it was only giving me credit for about 65% of my steps, assuming my pedometer is accurate.

    Today, I’ve moved the Flex to my left hand, and so far, it seems to me more accurate. Here are the current readings (almost 1 pm):
    Flex: 10134
    Ped: 12776

    This is about 80% — still well under what I would expect. I wonder if this is a bad unit? Mostly, I’ve seen reports of Flex over-reporting steps, not under-reporting.

  • blackSP

    As I stated numerous times on Facebook and the Fitbit ‘forum’ the Flex sucks.

    I stopped using it on the wrist as it over estimates around 30%. I mean 1 hour of guitar playing is good for at least 2000 steps. Bollocks! I’ve turned into a necklace and it’s now pretty good.

    Check here:

  • Bobbie

    Thank you for taking the time to do this.

    I’ve been wearing a Bodymedia Core armband, and finding that it routinely severely undercounts steps (I mean, I take my dog on a 3 mile walk and afterward the Bodymedia armband says I’ve taken less than 6000 steps ALL DAY when the walk alone should be in excess of that). I was worried that the Fitbit Flex would do something similar.

    It’s good to have a better sense of how these work. I’m not sure I’ll go with a Flex anyway, but it’s good to know that it’d at least be able to get a lot closer than I was anticipating.

  • Bobbie

    Manually logging means that you can go onto the Fitbit website and tell it that you did something that the device couldn’t see (whether it’s because you weren’t wear it, or because it was an activity that doesn’t measure well with this kind of item… like biking).

  • François Recorbet

    Thank you for all your comments. This makes the purchase decision much easier… I let you guess which one I’ll go for !

    • angelo212

      My guess is the “One”. Has to be as the results are better from my experience and hers. The Flex is not accurate.

  • tangyduc

    Hi, I can’t seem to find, is it possible to use both regularly? I love my flex, however, it doesn’t count stairs, I always have my Striiv on me as well, but it only has an Iphone app that syncs with the fitness rewards program I use so I still can’t add my stairs in. I have both, I just haven’t set up the One yet as I don’t want to give up my Flex.

  • Pamela Gremminger

    Have you tried to wear it around your ankle?

    • No, my ankle is too big, and it’s not really contoured for ankles, so it wouldn’t be very comfortable – let alone the fact that it would look like a house-arrest ankle bracelet 😉

  • Thank you very much for this comparison – buying this as a birthday gift so this was super helpful!

  • metric152

    This was a great comparison. I’d love to see the difference between a Force and the One. I have a One now and love it. I read the Force does a better job at tracking steps than the Flex.

  • rajasperson

    I recently bought Pocketband so that I can wear my One on my wrist. It hasn’t arrived yet. What are your thoughts on that? Do you think it will impact the One’s accuracy? I just keep forgetting to put it back on after I’ve changed clothes and thought that combining the best of both worlds might work!

  • panzer49

    I’m using the Force and to offset the sensitivity of its wrist-based nature (like the Flex) I wear it on my non-dominant hand and updated my settings to make Fitbit think it’s on my dominant hand. This decreases the sensitivity and I think gives a more accurate step count.

  • Martha B

    I have been wearing the “One” (and its previous incarnation) for several years. For the past couple of weeks I have been wearing the One and the “Force” (a gift) and I have found that the Force far exceeds the step count of the One (by thousands of steps a day for me). Interestingly it has a lower flight count than the One (sometimes by half). I will stick with the One for now because it seems a lot more accurate.

  • MH

    Thanks! Interesting. So do you have a final conclusion? Also, did you test the sleep feature?

    • I tried the sleep feature, but I didn’t compare it the same way I compared the steps.

      My conclusion is that the One is more accurate. This was written before the Force came out though, and I’m not sure if they have adjusted anything for the Force. I asked them on Twitter and they never replied.

  • stlgirl

    Best and most honest comparison yet. Just ordered my One! Thanks

  • modulo2pi

    The variance delta for «Drinks and dinner» in the table is not correct. Should be “-212”. Otherwise thank you for your report. It confirms my choice for the «Fitbit One» based on technical/algorithmic reasoning.

  • oceanstar11

    I have the flex, but I don’t find it comfortable to wear. Much of my physical activity involves going up and down stairs and carrying things in my arms. The flex doesn’t measure my activity for any of that, even when it’s very strenuous. Would the one measure those activities better?

  • Milton Styron

    I did the same thing until I lost my one again for the second time. I found that they were pretty close to each other. I also ensured that I told it was on my dominant hand. If I didn’t lose the one again, I would post my findings on this. So the real question is how likely are you to forget or lose the one.

  • Yeah, I think that any torso-based pedometers, in general, are currently more accurate.

  • Lori

    Took the fitbit out of the flex wristband. Wrapped it in a thin strip of vetrap tape and put it around my ankle, sock over it. Got on the treadmill for half mile. Watched step count on my phone. Counted steps perfectly and matched half mile reading on the treadmill gauge. I think wearing this on my ankle will give me a more accurate count. When I’m holding something, walking the dog, pushing a shopping cart, I’m not getting an accurate reading while wearing it on my wrist. Vetrap tape is comfortable. Used by vets on animals. Tape sticks to itself but not to skin or hair. Has a gauze-like appearance and comes in many colors.

    • Candy

      Now that is a GREAT idea!! Because there is no way the flex is counting accurately while pushing a shopping cart or when you’re carrying something in your hands while walking.
      They say on the website that it doesn’t count steps when you’re driving a car….so how in the heck would it know to count steps when you’re pushing a shopping cart?
      I could probably tuck it under my shoe laces and that would work too.

  • Michelle

    Currently I don’t do a lot of walking outside due to very icy roads. I mainly do workout videos throughout Beachbody so they are strenuous and very active. Will the one record this activity? Thanks!

  • Vik Tor

    The only bit missed in this comparison is the real steps count. Comparing results from two “average” counting devices and trying to guess which one will get closer to reality doesn’t look much more accurate than reading adverts and trust them.
    I’ve been using Flex and found it not bad considering sleep monitor and food/drink intake count as well
    As I said these are average counters working on algorithm more or less sophisticated to determine whether the “shaking” recorded was a step or a burp. Not relying much on the reading but looking at trends put things in the right perspective and % variations in your summary table are not that big (as a trend).
    Same for “very active”, “active” and “calories”; steps counting doesn’t says if you are carrying anything or walking short/long steps, high hill shoes, against wind, … all things that can make a huge difference in activity effort and calories.

    When been lazy in a day no need to look at the Fitbit dashboard to know it and 500 very active handshaking won’t make any difference other than shoulders strain.
    But when after 2 months recording is always on 500 steps/d on average probably something need some adjustment (FlexBit or lifestyle)

    ps: forgot to tap “sleep” on your flex? log it later in your dashboard.

  • Marcusfacius

    I loved this article, thanks for posting it. Would love to see the same data with the Flex set to dominant hand, but being worn on the non-dominant hand (to reduce sensitivity).

    Also, I have a force, not a flex, but presumably they detect motion similarly. I do most of my running on a treadmill so I know exactly how far I’m going. I took time to calibrate my running step length really carefully, and I’m getting distances that are mostly under 0.5% different from actual, provided I run at/near the speed at which I calculated my running step length (for example 14.24 fitbit vs 14.29 treadmill, 12.97 on fitbit vs. 13.0 treadmill, 15.25 fitbit vs 15.38 treadmill, etc). For that application, it would seem hard to beat the force (and presumably flex). But yes, definitely while washing dishes, packing a bag, etc, the force can be fooled. It is just so convenient not to have to think about taking it off or putting it back on.

  • I am looking at both of these. I appreciate the science that you put into your discussion and review of the both of the bitbit devices. Great work.

    • Glad you found it helpful!

  • I believe I did switch and there was still considerable variation. If you run on a treadmill, where your arm movement is easily calculated, I think that makes sense. My treadmill (a magnetic, non-electric one) is harder to walk on without holding on. (It’s dumb – the angle is steep enough and non-adjustable, so I basically have to hold on to prevent falling off.) That means that what would otherwise be really easy to measure just isn’t. Also, I’m not really interested in it measuring the things that are already easy to measure. I’m more interested in it measuring things that are harder to quantify. Walking back from the grocery store with my hands full, walking the dogs, walking when it’s cold out and I have my hands in my pockets, etc. Calculating “normal” activities seem to suffer with the Flex, in my experience.

  • cindit0

    this was posted awhile ago, but I’m hoping you might still answer my question about your trials with both… did you sign up with two different fitbit accounts – one for each device and then sync them on separate mobile devices? Was wondering how you did it since I wanted to run a side by side myself and it tells me I can only replace a device on my account and not have two active at the same time.

    • Two accounts, one syncing to my phone, the other syncing to my tablet. (Sorry if that came through twice.)

  • Lula

    Thank you for this awesome review, I have the One and was just about to “upgrade” to the Flex, and now I won’t be. The only draw was the wrist band so I don’t lose the One, but other than that, I love that I don’t have to check my app for stats and I’ve found the One to be super accurate.

  • Menotu2

    I wish the article showed a picture of each

  • uniquename72

    Thanks for this! I’ve resisted buying any of these devices because I do most of my walking/running with a dog, and assumed it wouldn’t count my steps properly.

    Apparently BOTH devices you tested did well in dog walking. Nice!

  • jlr123

    I wish I’d seen your review before I went and wasted money on the flex today. I’m wearing it on my non-dominant hand, and I noticed it recorded at least 10 steps while I opened a package. It’s also a lot bulkier than I thought it would be (hopefully I will get used to this) I was afraid of forgetting/losing the one, so that’s ultimately why I went with the flex.

    • Ncjayhawk

      My daughter wears her One on her bra as recommended and did lose it once. I wear mine on my bra but not at the center I wear it close to the strap instead of the center and it stays well.

  • T Thomas

    THANK YOU for the AWESOME review! I have them both in my Best Buy cart and was wondering which one to choose. Based on your review, I’ll be going with the one!!!

  • sandy

    Very interesting, I debating which unit to get when I upgraded from the zip and went with The One, wasn’t sure I wanted to wear a band all the time. Looks like I made the wise choice.

  • Phyllis Jean Haws-Garard

    Thanks for the great testing I have been waering the fitbit zip and have been considering adding one that tracks my sleep also I wear mine on my waist so wasnt sure I wanted one that could only be worn on the wrist and I like seeing my steps thoughout the day and you cant with the flex so you have helped me with that decision

  • lindygirl

    Thank you very much for the awesome post, and sharing the analysis of your data. I have the One, but sometimes wear it in the armband, if I’m wearing a dress that doesn’t require a bra (it happens more often than one would think). I’m trying to determine how using a torso-based pedometer on the arm will affect my daily step numbers. Any ideas, short of buying another One and running a test similar to yours?

  • Ginger71

    my flex is very accurate, i have tested it many times watching my phone as i step and every step i take it moves one and it doesn’t move when i don’t move. So im very happy with my flex

    • I’m glad you’re happy with your flex, however my data is accurate, so…

      • The question was never about whether it counts steps, it was about counting things that aren’t steps as steps, or having issues like when your hands are full so your arm doesn’t swing. I’m glad it’s working out for you, however I stand by the data I collected, and my assertion in the article based on my own use cases.

  • Pixie Mellott

    Very interesting!! I did the same thing with a spreadsheet and hourly data updates when I first got my Flex and the numbers were so different than with my original FitBit Zip. I found that I was getting gyp’ed on tons of steps when walking my two boxers for their 3 mile walk because I don’t move my arms while hold their leashes. Overall, I prefer the Zip. Unfortunately, my Zip recently poop’ed out so I’m back to the Flex. I’m considering going with the One as an upgrade to the Zip.

  • grayce

    I find it interesting that a positive attribute of the flex is “lives on the wrist.” I cannot wear jewelry at work, so this is a negative for me. Many professions do not allow jewelry. I think the bracelet attribute is subjectively positive or negative. I often see this assumption of a bracelet being better on message boards. I hope manufacturers do not follow these comments for those of us who cannot use a bracelet.

    • Sorry for the late reply. The reason I cite the Flex being on the wrist as a positive is simply because it’s harder to lose, not for any other reason.

  • Roger

    This article is what the internet is all about; informative well-researched, well-written. The only downside is that I wished I had read it before buying the Flex. I have the One, but have lost two outright, so bought the Flex to solve this. Now I am not so sure, but thanks for posting the article!

  • Anushka

    Thank you very much…. What a helper this has been …. Thanks again!!!

  • Susan Fournet Blakely

    I wonder what the difference would be for the One with clipping it on the bra vs waist.

    • I don’t imagine it would be much of a difference. Both are spots on your core trunk, so the movement variations shouldn’t vary a lot.

  • Alicia Mathews

    Thanks for the review. Was leaning toward the One anyway because I don’t want to wear a wrist band 24/7. Definitely going with the One. I would rather the counts be under than over. Does the One come with a sleep band?

    • It comes with a wrist sleeve thing that you can tuck the One into and velcro around your wrist while sleeping.

  • Charlie

    Thanks for a brilliant review backed up by a spreadsheet. It confirms my results. I have a fitbit and bought my wife a flex. She was trouncing me on steps and when I looked into it I estimate the flex was reading 20 to 40% high. We have returned the flex and got a refund as I dont believe it is “Fit” for purpose.

  • tuneplayer

    Great review! What it makes me think, though, is that even if your chosen device over- or under-reports activity, if it’s consistent over time, you can still gauge your own level of activity against your personal history….. what your more and less active days are, whether you are becoming more or less active as a trend. If your device over-reports, just set your goal a bit higher proportionately.

    [I use my One (& formerly Ultra) clipped to my bra – on the left upper part of the cup, sort of just adjacent to my armpit. Not their recommended place but works for me.]

  • Thanks, very useful information. I wish it had included something about the sleep modes, since improved sleep is my primary interest. Pretty strongly leaning towards buying the One at this point, but I’m also hoping to get some comparative activity data from the pedometer in my smartphone and from my Omron HSL-101 sleep meter…

    Interesting that several of these devices have some integration with weight, but I’d be more interested in integration with blood pressure, especially continuous blood pressure. However, in terms of pie in the sky, I wish they had annotation features. For example, you could add a code for “ate spicy food for dinner” and if it sees a similar sleep pattern on another night, then it would ask if I want to add the “spicy food” annotation to that night’s sleep. Of course that would be even better for the continuous blood pressure data, but evidently that’s still too experimental… (It sounds like Apple was considering including such a sensor in their new watch device, but pulled back.)

  • guest

    This has been the most helpful review – by far!! Thank you.
    I am looking at the ‘One’ v/s the ‘Flex’. I have one more question – the comparison chart shows that step calculation is only feature not present in the flex. All things considered and equal, and going by comments below, would you recommend the one over the flex? They are at the same price point and I am confused. Looking forward to your advice. Thanks, Anu

    • Do you mean stair step calculation? I guess it sorta depends on whether you climb a lot of stairs. I didn’t, so it wasn’t as important to me.

  • steph

    I hat a plain ‘ol Fitbit and found that it would fall off on my bra so just clipped it to my watch band and it seemed to do great there—anybody else try that? I wonder how it would be with data recording since the wrist location seems to “over count”… Unfortunately the back was lost after changing the battery and I don’t know how to buy a new back so am now having to try to decide if I should “upgrade” or not.

  • Zara

    They should of made them as anklets not bracelets that would have been spot on accutate

  • disqus_Gn2ZYhtRs7

    I had a fitbit flex and stopped using it because I’m left handed. I know there is a “dominant” and “not dominant” mode, but I eat and write with my left hand, while I open doors, use a mouse, use scissors, and anything else made for right handed people with my right hand. How is it supposed to track that when I am essentially ambidextrous for the fitbit’s measurements? The other fitbits don’t work for me, purely because I would forget to put them on. The attraction of the flex was I didn’t have to worry about remembering it.

  • Cynthia Silva

    This is a great review! You’ve made my decision to stick with the fitbit One an easy one!!
    Also glad to read that your a tech GIRL! we need more tech savvy chicks doing review for all things technology! Rock on!

  • Kris Angaran

    I am trying this experiment as well. This is day one and so far the one is 700 steps higher. I have the one on my bra and the flex on my non dominant hand. Why do you think the one is higher?

  • Stormy HotMoma Tanner

    I love your detail, thank you!

  • Alison

    I just found this post because I’ve recently got a flex for exactly the same reason as you (I lost my Fitbit One) and could see straight away there were real differences in terms of how each measures walking. I’m walking the same amount each day but reach the 5 mile target a lot earlier. I remember when I had the FT One that if you watched your phone display while you were walking (not advisable for very long, and also a bit sad) you could clearly see that one real step = one recorded step. When I did this with the Flex it was recording steps faster than I could walk them. I’m a bit disappointed with it really – I might try a Zip next time as I also don’t like the look of the Flex either..

    One thing – I wonder what would happen if I just put the gizmo in my trouser pocket? I might try that one day just to see. I’d lose it pretty quickly however so it isn’t a good long term solution.

    And one other thing – for anyone reading this and thinking ‘right I’ll just go and buy a Fitbit One’ – they are very easy to lose. If you wear trousers all the time you’re ok, but if you wear skirts/dresses etc and have to attach it to your tights/wasteband – it won’t last long…

  • Michele

    I found this to be the problem when it was on my dominant hand. So I switched and now it’s extremely accurate. I’ve tested it and I actually have to walk or simulate walking while before on my dominant hand it was super sensitive.

  • nursenjm

    I have used flex for a year, wear it on my ankle as I just wasn’t getting accurate arm readings. Cute bands from etsy. It is very accurate according to map my walk comparisons.

  • Jane Rafe

    Hey Snipe! love this clear article. When people say ‘One’ is easy to lose, is it cos the clip is poorly made or because they forget it’s there and chuck it in the washing machine? I’m interested in buying one but I can’t afford to lose and replace on a regular basis as some people seem to have done!

    • I definitely wouldn’t call it poorly made. It’s very sturdy, and I’ve never had one break – but for me, leaving it clipped to my jeans would result in it falling off due to general jostling, while when it was clipped to my bra, it would usually fall off only if I clipped it in the middle between my boobs. (I am quite busty, so there’s a lot of underwire and such that the clip had to work around.) When it was clipped to my should straps, it wasn’t such a big deal, but it could look weird through clothing.

      I’ve thrown mine in the wash by accident and it weathered it just fine.

      • Rebecca Hogg

        The poorly made part of the clip is that little piece at the end. I’ve had a One for almost 3 years and I’ve had to replace my clip 5 times because that piece comes off the clip and there are two little metal stabby ends there. I have recently found a new clip that I’m hoping is made a little better. At the least it’s cheaper, so replacement is much easier to come by.

        I also wear mine on my bra strap and it has weathered fine through the wash a couple times.

  • BK

    Nice job on the article. I’m gifting my Fitbit One to my daughter, having upgraded to an Apple Watch/iPhone 5S for tracking steps. I wanted some data comparing a wrist worn device to one clipped to the waistband (which would surely be lost). Your data is exactly what I was looking for to guesstimated the differential of additional steps from wearing it on the wrist. Well done!

  • Dawne

    Thank you for this post. It’s very helpful now that I’m contemplating my first purchase of a FitBit product.

  • Janie Way Grohs

    Can I put my tracker from Fitbit flex in the Fitbit one holder and wear on belt or bra?

  • Maria Gutierrez

    Have you tried changing the “dominant” setting to “non dominant?” It is supposed to make the Flex less sensitive. Also, maybe changing it from one hand to the other? For example, if you are right handed change it to the left, since you are less likely to do things with that one. I’m considering upgrading from a Zip to the Flex, so I’m going around reading reviews about it.

By snipe
Snipe.Net Geeky, sweary things.

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I’m a tech geek/dev/infosec-nerd/scuba diver/blacksmith/sword-fighter/crime fighter/ENTP/warcrafter/activist. I run Grokability, Inc, and run several open source projects, including Snipe-IT Asset Management. Tweet at me @snipeyhead or read more...

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