What elevation gain actually means on a hiking app

Gain, loss and net change

Take the sequence of elevations along your route. Walk through it in order. Every time the elevation goes up between one point and the next, add the difference to a running total; when it goes down, add it to a separate one. The first total is cumulative elevation gain, sometimes called total ascent or simply climb. The second is elevation loss. The difference between your start and end altitude is net change, and it is a different and much less useful number.

For an out-and-back walk, gain and loss are close to equal. For a point-to-point traverse they can be wildly different. For a loop, net change is zero by definition while gain can be enormous. When someone says a route is "800 metres of climb", they mean gain.

Where the elevation numbers come from

GPS altitude

Satellite positioning produces a vertical figure as well as a horizontal one, but vertical accuracy is inherently worse — typically by a factor of two or three — because the geometry of satellites overhead constrains height less well than it constrains position on the ground. Raw GPS altitude wanders by several metres even when you are standing still.

The barometer

iPhones from the 6 onward include a barometric pressure sensor, and pressure changes with altitude in a well-understood way. This gives much smoother relative altitude changes — excellent at detecting that you climbed ten metres — but it needs a reference, because pressure also changes with the weather. A passing weather front can shift the apparent altitude by tens of metres over a few hours with you standing still.

Terrain models

Some services throw away your recorded elevation entirely and look up the terrain height at each coordinate in a digital elevation model. This is very stable and completely blind to bridges, tunnels and multi-storey anything.

Why two apps disagree about the same walk

Because every one of them applies a filter, and the filters differ. Consider a completely flat walk recorded with noisy altitude data that jitters plus or minus three metres between points. Add up every upward jitter naively and you have "gained" several hundred metres without leaving the valley floor. Every app therefore ignores changes below a threshold, and that threshold is a judgement call — commonly somewhere between three and ten metres. A lower threshold reports more gain; a higher one reports less.

This is why the same GPX file uploaded to three services returns three different climb totals, all of them defensible. The lesson is to compare your walks against each other within one app, and to treat cross-app comparison of elevation as approximate. Distance is far more consistent across tools; elevation is the number to be sceptical about.

TrailCam shows elevation gain as a profile drawn under the map, alongside distance, moving time and pace, and the same profile runs underneath when you replay a saved route.

What the number is good for

Elevation gain is the best single predictor of how hard a walk will feel, far better than distance alone. Ten kilometres on the flat and ten kilometres with a thousand metres of climb are not remotely the same afternoon. Long-standing rules of thumb in hill walking add roughly an hour to the estimated time for every 600 metres of ascent, on top of the time the horizontal distance would take. It is crude, and it is still more useful than judging a route by its length.

It is also the honest way to compare two routes of similar length, and the reason a modest local hill can be a harder day than a much longer valley path.