Air pressure drops by about 1.2 hPa for every 10 metres of altitude.
That's roughly 1 hPa per floor. Your phone's barometric sensor is sensitive
enough to detect this — and sensitive enough to detect you walking up a flight of stairs.
every ride-hailing app tracks which floor of a building you're on.
Uber, Lyft, and Google Maps use the barometer to know whether you're in the lobby
or on the 12th floor — so the car meets you at the right entrance.
Insurance apps use the same data to detect whether you're in a hospital.
None of this requires GPS. Altitude works indoors where GPS doesn't.
—
estimated floor
waiting · tap start sensor
—hPa
—rel. altitude m
—trend hPa/s
current pressure—
baseline (ground floor)not set · press "set ground floor"
altitude change—
▶ how does this work?
Atmospheric pressure decreases predictably with altitude — the barometric formula.
Near sea level, each 8.5 m of altitude corresponds to roughly 1 hPa of pressure drop.
A typical floor is 3–4 m, so that's about 0.35–0.45 hPa per floor.
Modern phone barometers have a resolution of 0.01–0.06 hPa — enough to detect
a single floor change. They update at 1–50 Hz depending on the device.
The sensor is used by Apple's iPhone to track floors climbed in the Health app.
The Barometer API (part of the Generic Sensor API) is available in Chrome on Android.
If unavailable, a prompt will appear. On iOS, pressure data is not directly exposed to web apps.