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]




Previous post

Make or Buy The Internet from "The IT Crowd"

Next post

Failing Well: Managing Risk in Web Applications



I’m a tech geek/dev/infosec-nerd/scuba diver/blacksmith/sword-fighter/crime fighter/ENTP/warcrafter/activist. I'm the CTO at Mass Mosaic and the CEO of Grokability, Inc. in San Diego, CA. Tweet at me @snipeyhead or read more...

  • 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…

  • 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.