Free trail calculator
Trail race time calculator and km-effort
Enter your race's distance and elevation gain: km-effort tells you what it really weighs. Add a race you have run to estimate your finish time.
- Km-effort
- 45
- Density
- 50 m/km
- Estimated time
- 4h 58m
- Pace per km-effort
- 6:37
- For the Uptrail engine
- Short trail (under 42 km)
- Recovery planned after the race
- 21 days
Km-effort in one line
One extra kilometre for every 100 m of climbing. A 40 km trail with 2,000 m of gain weighs like 60 km on the flat. It is the ITRA convention for comparing races that look nothing alike on a map, and the measure Uptrail's engine uses to estimate a race's duration and size the recovery after it.
How the estimate is computed
Your pace per km-effort
Your reference race's time divided by its km-effort gives your base pace, climbs included.
A slowdown with duration
Nobody holds the same pace over 60 km-effort as over 30. The estimate applies Riegel's endurance formula (exponent 1.06), the standard of running time predictors, to km-effort instead of kilometres.
What it does not see
Technical terrain, heat, night, altitude and fuelling. On ultras past 100 km the slowdown is often steeper than the formula predicts: read the estimate as a floor.
Questions about km-effort
What trail runners ask before they pick a race.
The distance in kilometres plus the elevation gain divided by 100. A 30 km trail with 1,500 m of gain is 45 km-effort. It is the measure ITRA uses to compare races.
It is a convention, not a law of physics: on average, climbing 100 m costs about the time of a flat kilometre. It slightly overrates gentle runnable slopes and underrates technical terrain, but it remains the best simple tool to compare two courses.
Not in km-effort. Descending still wears the quads out: in Uptrail, your race's elevation loss triggers eccentric work when it really matters (25 m of loss per km, or 1,500 m in total), on races of 42 km and more.
It is an order of magnitude. It gets closer the more recent your reference race, the closer its length and the more similar its terrain. For a first ultra, aim slower.
The engine starts from your race's distance and elevation gain to estimate its duration for your level, size the long run and the taper, and plan the recovery after the line. The plan is built on them, then reworked when a key session falls through.
Your race has a km-effort. So does your plan.
Enter your race, its elevation and the days you can run. The block is built on it, then reworked when a key session falls through.