Grade adjusted pace (GAP)
What it answers
You ran 6:00/km up a 5% hill. What pace on flat ground would have cost you the same? That flat pace is your grade adjusted pace, or GAP.
Type the pace you held and the grade. The big number is the flat pace with the same effort. Uphill it comes out faster than what you ran, downhill slower. The distance field only changes the drawing of the hill.
If you have saved your training zones, the result also tells you which zone that effort lands in.
Where the numbers come from
The calculator uses the energy cost of running on slopes that Alberto Minetti’s team measured on a lab treadmill, published in 2002. Holding 6:00/km up a 5% grade costs what 4:37/km costs on flat.
Climbs get expensive fast. At 10% you pay about two thirds more energy per kilometre than on flat.
What people get wrong
Holding flat pace on a climb. At 5%, your 6:00/km easy pace costs what 4:37 costs on flat. The run stopped being easy at the bottom of the hill.
Treating downhills as free. The model counts energy and nothing else. Energy cost is lowest around -20% and rises again past it, and the calculator follows that. The pounding your quads take on a steep descent never shows up in the number.
Expecting it to match your watch or Strava. Every app uses its own model, so their GAP will differ from this one, most of all on steep grades.
Using it
On a hilly easy run, run by feel or heart rate, then check the GAP afterwards to confirm the day stayed easy.
For a hilly race, try your goal pace at the grades on the course. The GAP shows what each climb will really cost, which is a better guide than holding the same pace all the way.