A grade adjusted pace calculator converts a pace run on a hill into the flat-ground pace that takes the same physiological effort. Running uphill costs more energy per unit of distance than running flat, and running gently downhill costs less, so the same watch pace means a different effort depending on the grade. GAP strips the grade out and expresses everything as an equivalent flat pace.
This calculator uses the Minetti, Moia, Roi, Susta and Ferretti (2002) gradient-cost polynomial, published in the Journal of Applied Physiology from treadmill oxygen-consumption data across minus 45 to plus 45 percent grade. It gives the energy cost of running at any gradient relative to flat ground, then scales your pace by that ratio to find the flat-equivalent effort, or scales a flat goal pace up to a hill target pace.
By the Minetti model, a 5 percent uphill grade costs about 30 percent more energy per unit distance than flat ground. So running 5:00 per km on a 5 percent uphill grade takes roughly the same effort as running about 3:51 per km on flat ground. Put the other way, if your flat goal pace is 5:00 per km, holding the same effort on a 5 percent uphill means slowing to roughly 6:30 per km.
Yes. The Minetti polynomial covers grades from minus 45 to plus 45 percent, so gentle downhill grades show up as a lower energy cost than flat. For example, a 5 percent downhill grade costs roughly 24 percent less energy than flat, so 5:00 per km actual pace downhill is roughly equivalent in effort to about 6:33 per km on flat ground. Very steep downhill grades raise the cost again in the model, from the extra muscle braking needed to control the descent.
The Minetti polynomial is the standard reference behind grade-adjusted pace tools industry-wide and models aerobic energy cost from gradient alone. It does not account for footing, turns, sustained downhill muscle damage, heat, wind or fatigue late in a race, so treat the result as a useful training and pacing estimate, not a race-time guarantee.
This calculator takes one grade you type in and converts one pace, useful for a single hill, a treadmill incline or a training segment. The Marathon Course Difficulty Comparison and Time Converter integrates the same Minetti formula over the real, published elevation profile of each of the eight Marathon Majors, so you can convert a finish time from one Major to its elevation-adjusted equivalent on another.