What Size Fitness Tracker Should You Buy

Getting the correct size of tracker for your wrist is important. You want the tracker to fit so that if it measures accurately and features like an optical heart rate monitor work effectively. Equally, you don’t want it so loose that you are in danger of it falling off or getting lost. In this post we hope to help you get the right size for you.

In general, you want the fitness tracker to sit flat on your wrist. Most manufacturers provide a sizing guide or you can use a piece of string to measure your wrist and buy the appropriate one for your wrist size. There’s a photo above showing what a good fit should look like. Of course, some people like to wear watches and bands a little looser. It’s a personal choice.

Getting the correct tracker for your wrist size

Where to wear

If you want the tracker to measure your sleep the chances are that you will be wearing it all the time. As such it is really important to get a comfortable fit. In general, you want to wear your fitness tracker as you would a normal watch, which means it needs to be worn around 1-3 finger widths from your wrist bone and lay flat.

What size do I need

Wrist size

The key to getting the best fit is wrist size. Below we have listed average wrist sizes at various ages to give you a guide.

Age Average wrist size (inches) Average wrist size (cm)
18 months old 4.5 11.5
> 5 < 7 years old 6 15
> 9 < 12 years old 6.5 – 7 16.5 – 18
> 13 < 19 years old 7 – 7.5 18 – 19
> 19 years old 7.5 19

Of course these are just averages. Numerous factors can mean these are way off and it makes much more sense to measure your own wrist.
There are 2 sensible ways in which this can be done

1) Manufacturer sizing guide

If you have in mind the manufacturer of your fitness tracker they sometimes provide a handy sizing tool. You then use these to measure your wrist and identify what size from that manufacturer you need. We have linked to some of the more common ones in a table below

2) Measure your own wrist

There are 2 ways you can do this. Get an old fashioned tape measure and wrap it around your wrist or get a piece of string / shoelace and wrap it around your wrist then measure it with a ruler. Ideally, you need to measure the wrist on your non-dominant hand.

So if you’re left handed your right wrist and vice-versa. You want to make sure that it is secure and not too tight so it can get the best readings when you exercise. Also if you are on the boundary of two sizes always get the better one. It will be easier to adjust a larger one to make it smaller. Not so much the other way round.

Once you have your wrist size it should translate to a size in the tracker of your choice. Different trackers can have different sizes. As such you need to make sure you check the manufacturer’s websites. However, for illustrative purposes we have included some examples.

Manufacturer Model Tracker size Tracker Size Wrist size (inches) Wrist size (mm) Sizing guide
Fitbit Versa Small 5.5 – 7.1 140 – 180 Sizing guide
Fitbit Versa Large 7.1 – 8.7 180 – 220
Fitbit Ionic Small 5.5 – 6.7 140 – 170 Sizing guide
Fitbit Ionic Large 6.7 – 8.1 170 – 206
Fitbit Charge 2 Small 5.5 – 6.7 140 – 170 Sizing guide
Fitbit Charge 2 Large 6.7 – 8.1 170 – 206
Fitbit Charge 2 X-large 8.1 – 9.3 206 – 236
Fitbit Alta / Alta HR Small 5.5 – 6.7 140 – 170 Sizing guide
Fitbit Alta / Alta HR Large 6.7 – 8.1 170 – 206
Fitbit Alta / Alta HR X-large 8.1 – 9.3 206 – 236
Fitbit Flex 2 Small 5.5 – 6.7 140 – 170 Sizing guide
Fitbit Flex 2 Large 6.7 – 8.1 170 -206
Garmin Vivoactive HR Regular 5.39 – 7.68 137 – 195 Sizing guide
Garmin Vivoactive HR X-large 6.38 – 8.86 161 – 225
Garmin Vivosmart Small 5.0 – 6.8 127 – 172 Sizing guide
Garmin Vivosmart Large 6.1 – 8.7 155 – 221
Garmin Vivofit Small 4.7 – 6.9 120 -175 Sizing guide
Garmin Vivofit Large 6.0 – 8.3 152 – 210
Samsung Gear Fit 2 Pro Small 4.9 – 6.5 125 – 165
Samsung Gear Fit 2 Pro Large 6.2 – 8.0 158 – 205

Other things to consider

  • The size of the tracker unit

    Although not as important as the size of the band the size of the actual tracking unit should come into consideration also. Make sure that you get one that you are
    comfortable with. Some of the more modern smartwatches and trackers come with all sorts of tech wizardry like GPS and contactless payments. This can all add to the size of the unit itself so be sure to take it into consideration when you are considering what size to buy

  • Replacement straps

    Some but not all fitness trackers have replaceable straps. These are great if you’re not sure or you have lost or gained a bit of weight. Simply order a replacement band or band extender to meet your needs and you’re good to go

  • Rashes

    Having your fitness tracker too tight can contribute to soap getting stuck between the strap and your wrist. Make sure there is enough wiggle room to let your wrist breathe. Also, if you are interested in this topic be sure to check out this article about what to do if your fitness tracker gives you a rash.

Non wrist worn trackers

If you’re the kind who doesn’t like to wear things on your wrist maybe size won’t be an issue. There are other fitness trackers such as the Fitbit Zip, Misfit Ray and which can be worn on your body or inside special jewelery


The size of your fitness tracker you need is dependent on a number of factors. You need to take into consideration the circumference of your wrist, the manufacturers recommended sizing and whether your wrist is likely to be losing or gaining inches over the time you have the tracker.
Once you have all that information you can look at trackers that you like, that match your size and needs. The only thing we would recommend is that if you are on the cusp of 2 size brackets always go for the larger size.
As well, don’t forget that if you go for a tracker with interchangeable straps you could potentially mix and match the bands to get your own custom size.

If after all that you are still unsure don’t forget that many local stores have Fitbits for sale and you can go and try one on for fit.