You walk around the city, and in the evening the app shows you so many kilometres. But the band has no satellite navigation and does not draw your route on a map. So where does that number come from? Let us work it out — then you will know what to trust and where a small error is possible.

Distance is steps multiplied by stride length

The band measures movement, not distance: the optical sensor on your wrist and the motion sensor catch every step. The app works out distance itself, on a simple idea:

number of steps × length of one step = distance covered.

The app does not invent your stride length. It takes it from your profile — from your height and sex. The logic is everyday: the taller the person, the longer the stride. That is why the band needs no satellites to estimate how far you went.

Why accuracy depends on your profile

Since everything rests on stride length, so does accuracy. If your profile has the wrong height, the stride shifts — and the whole distance drifts with it.

  • Set a height lower than yours and the kilometres come out short.
  • Set it higher and the number grows instead.

So it is worth checking once, calmly: are your height and sex correct. It is the simplest thing you can do for honest numbers.

Why the numbers do not match a map exactly

Sometimes the app shows one thing and the map on your phone shows something slightly different. That is normal, and here is why.

Your stride while strolling and while running is different in length. When you run you reach further and the stride widens. The band works from an averaged length, so on a run small discrepancies are possible: here it undercounts a little, there it adds a bit.

So take distance calmly — it is an honest estimate, not a measurement to the metre. And look not at a single trip to the shop but at the trend: how your activity changes across the week. That is where everything important hides — whether you started moving more, whether you came back to walking, whether the habit is getting stronger.

Sources

  • More daily activity, lower mortality — Ekelund U. et al., BMJ, 2019. read
  • Accuracy of steps and distance on wearables — an umbrella review — Doherty C. et al., Sports Medicine, 2024. read

This is not a medical device: distance figures are a reference for watching your own activity, not a precise measurement and not a basis for health decisions.