Elevation gain is one of the most useful numbers for judging how hard a hike will be — and one of the easiest to get wrong. Here’s exactly how HiiKER works out total ascent and descent, and why the figure you see in HiiKER can differ from your watch or another app.
In this article: Where the heights come from · The 6 m rule · Why use a threshold? · While you’re recording · Why HiiKER and Garmin disagree
Where the heights come from
- Planned routes and HiiKER hikes — we read the height of the ground at points all along the route from a digital elevation model (DEM): a detailed map of the height of the land.
- Your recordings — while you walk, your phone records its own height reading with every GPS fix. When you save a recording and it uploads, HiiKER looks up the ground height for every point from the same elevation model and recalculates the totals. That’s the figure you see on your saved recording.
The 6 m rule
Height data is never perfectly smooth. A few metres of wobble between neighbouring points is normal, from both GPS and terrain data. If we added up every tiny rise, a flat path would gain height it doesn’t have. So HiiKER measures from a moving baseline:
- The first height on the route is the baseline.
- HiiKER works along the route point by point.
- A rise only counts once it’s more than 6 m above the baseline. When it is, the whole rise is added to your ascent, and the baseline moves up to that point.
- Whenever the route drops below the baseline, the baseline drops with it — however small the dip — so the next climb is measured from the bottom.
Descent works in exactly the same way, in the opposite direction. Using one rule both ways keeps the totals consistent: on a loop that finishes where it started, ascent and descent come out the same, or very close.
An example: a path goes 100 m → 104 m → 98 m → 109 m. The rise to 104 m is only 4 m, so it isn’t counted. The dip to 98 m moves the baseline down. The climb to 109 m is 11 m above that, so 11 m is added — 11 m of ascent in total. Adding up every rise would have given 15 m.
Totals are rounded to the nearest metre. The same rule is used on hiiker.app, in the iPhone and Android apps and in HiiKER’s watch apps, so a route shows the same figures wherever you look at it.
Why use a threshold at all?
Adding up every rise between neighbouring points — the method this post used to describe — reads around a quarter too high on real trails, and can turn a level canal towpath into hundreds of metres of “climbing” that isn’t there. A 6 m threshold filters out that noise while still catching real climbs: once a climb passes 6 m, all of it counts.
The trade-off is that a series of very small ups and downs, each under 6 m, isn’t counted. On gently rolling ground that can make HiiKER’s figure a little lower than an app that counts everything.
While you’re recording
The live ascent figure on the recording screen comes from your phone’s own height readings, which are noisier than terrain data:
- iPhone and Apple Watch — the same 6 m rule, applied to the readings as they come in.
- Android — HiiKER first ignores readings the phone marks as inaccurate (vertical accuracy worse than 15 m), smooths the rest over five readings, then counts climbs of more than 10 m. That keeps the live figure steady, but it usually reads a little lower than the final one.
Once the recording is saved, its totals are recalculated from the elevation model as described above, so the number on your saved recording can differ slightly from the one you watched during the walk.
Why HiiKER and Garmin (or other apps) disagree
Every app measures elevation in its own way, so two apps can show different totals for the same walk. The usual reasons:
- Different height data. Many Garmin watches measure height with a barometric altimeter, while HiiKER’s saved figures use terrain data. Each has its own errors: a barometer drifts as the weather changes, and terrain data can smooth over small features such as a short, steep knoll.
- Different noise filters. Garmin and other apps apply their own smoothing and thresholds. A bigger threshold gives a lower total; counting every rise gives a higher one.
- Different tracks. A GPS track that cuts corners or wanders off the path samples slightly different ground.
Differences are usually biggest on flat or gently rolling routes, where lots of small ups and downs are either counted or filtered out depending on the method.
If a figure looks clearly wrong — say, hundreds of metres of climb on a flat route — let us know, with a link to the hike or recording.
If you have feedback on this method, please let us know.
Related: Hike time settings: what they mean and how to change them.
