Why your Apple Watch flights climbed number is wrong

Your watch is not counting stairs. It reads air pressure through a small vent in the side of the case, turns the change into height, and scores a flight for about every ten feet it thinks you climbed on foot. Nearly every wrong number comes from something that changed the pressure while you were not climbing, or something that stopped the watch reading it.

What it is actually counting

Apple’s own developer documentation describes the figure as the approximate number of floors ascended by walking. Two things follow. Standing on an escalator or riding a lift should not count, because you are not walking. Walking up a steep street or a trail does count, because ten feet of hill is ten feet of climbing. A flight works out to about 16 stairs, whatever the staircase looks like.

When the number is too high

A barometer cannot tell the difference between you walking upward and the air pressure around you dropping while you walk. Weather moves pressure all the time. In January 2021, Apple Watch owners in Germany reported their watches reading altitude 200 to 300 metres too high during a spell of low pressure. Those were user reports, not an Apple statement, but the mechanism is the same one every barometric tracker has.

Fitbit says it outright for its own devices, which count floors the same way: a gust of wind, a change in the weather or opening a door can register extra floors. Apple has not published an equivalent list, but an Apple Watch uses the same kind of sensor, and there is no reason it would be immune.

Why it only ever goes up

Climbing and descending are counted separately, and going down never subtracts from going up. So pressure noise is lopsided. A dip that looks like climbing adds a flight; the matching rise that looks like descending does not take it away. Over a stormy week the errors pile up in one direction instead of cancelling out, so the number drifts high rather than low.

When it is too low, or zero

Water is the usual cause. Apple’s water-resistance page says the barometric altimeter can be less accurate if water gets into the air vent, for example while swimming, and that it returns to normal once the water has evaporated. If it reads zero on the day after a swim, wait for it to dry before worrying.

The rest are working as designed. A StairMaster keeps you at the same height, so an hour on one adds nothing. A single storey of a house is about nine feet, a little short of one flight. And a lift does not count at all.

If the count sits in the dozens every day regardless of weather, and drying the watch changes nothing, that is not weather. Take it to Apple Support.

What it means for the number in Humblebrag

The app reads Flights Climbed straight from Health, so whatever the watch recorded is what the comparisons use. A single day after a storm can be a flight or two generous. Over weeks the climbs you really did dominate, but because pressure noise only adds, a total built from a barometer leans slightly high. It is the same ten-foot flight either way, just not always one you walked.