Live reading
Your browser knows where you are. This turns that into a height above sea level — and, unlike most pages that do this, tells you how sure it is.
Your browser asks permission first. Nothing is stored, and nothing is sent to us.
Decimal degrees — 47.796 and 12.983, for example.
Coordinates go to Open-Meteo (or, if it is unreachable, to Amazon’s public terrain tiles) to read the terrain height — nothing is logged by us or kept in your browser. Typed coordinates need no location permission at all. The privacy policy says it in full.
Three things stand between a pair of coordinates and an honest height. Most pages that answer this question mention none of them.
The height comes from a satellite radar model of the landscape. It knows the terrain well. It does not know that you are on the tenth floor, on a chairlift, or in a plane.
Satellites measure against a mathematical shape, not the sea. Near Salzburg the correction between them is about 46 m. Some phones apply it before the browser sees the number, and some hand it over raw.
At one point outside Salzburg, four public datasets return 434, 435, 435.1 and 437 metres. None of them is lying. A single number quoted to the centimetre is hiding that, not solving it.
Every number on this page is a fix: one place, one moment. What it cannot give you is change — the climb you actually made, metre by metre, while you were walking. Coordinates cannot see that reliably, and a browser has no access to the one sensor that can: the barometer already in your phone.
That sensor is what VERT is built around. It reads pressure rather than satellites, so it works in a gorge with no signal, it carries its own ± instead of pretending it has none, and it writes your day to disk as you walk — not when you remember to press stop.