Trail calculator: ITRA effort-km and estimated time
ITRA effort-km is calculated like this: distance in km + elevation gain in meters / 100. Enter the distance, the elevation gain and your usual pace on flat ground, and the tool gives you the effort of the race in effort-km and a first estimated time.
Fill in the fields to see the result.
How to use it
- Enter the distance of the trail race (in km or in miles) and its total elevation gain.
- Enter your usual pace on flat ground, the one from your easy long runs.
- Read the effort-km: it's the “flat” distance that represents the effort of the race.
- Read the estimated time, and treat it as a starting point for planning your fueling.
The method
The ITRA (International Trail Running Association) rule is simple: each kilometer counts as one effort-km, and every 100 meters of elevation gain adds one more. So a 30 km trail race with 1,000 m of elevation gain comes to 40 effort-km. ITRA uses it to rank races by difficulty and award its points. Downhill isn't part of the calculation.
For the time, the calculator multiplies this effort-km by your pace on flat ground. The idea: climbing 100 m costs about as much as one more kilometer on the flat. Minetti et al. (2002) measured that the energy cost of running rises sharply with the slope, which explains why a trail race with lots of elevation gain takes much longer than a road race of the same length.
An example
Your trail race is 30 km with 1,500 m of elevation gain. The effort-km comes to 30 + 1,500 / 100 = 45 effort-km. If you run your easy runs on flat ground at 6:00 per km, the estimated time is 45 x 6:00 = 270 minutes, or 4:30:00.
Limitations
The estimated time is a ballpark figure, not a prediction. The formula doesn't see the downhill (which wears out your thighs and slows you down on technical ground), the terrain (roots, scree, snow), altitude, heat, night or the fatigue that builds up over an ultra: on long distances, the real time is often longer. On the other hand, on very steep slopes, many trail runners walk, and the cost of climbing no longer follows the same rule. In miles and feet, the calculator converts: 100 m of elevation gain is about 328 feet, and effort-km stays a unit in kilometers. Before a first mountain ultra, medical advice can be useful if you have a history of heart problems.
Frequently asked questions
How do you calculate effort-km?
Add the distance in km and the elevation gain in meters divided by 100. A 42 km trail race with 2,500 m of elevation gain comes to 42 + 25 = 67 effort-km.
Does elevation loss count in effort-km?
No, the ITRA rule only counts elevation gain. Some hiking formulas add the downhill, but that's not the ITRA calculation.
How do you estimate your time for a trail race?
A simple method: multiply the effort-km by your pace on flat ground. It's a starting point. Then compare with your times on trail races you've already run, which take into account your downhill skills and how you handle technical ground.
What are ITRA points for?
They rank races by their effort-km, from 0 to 6 points. Some big races require a number of points to sign up.
Sources
- ITRA, International Trail Running Association (2024). Discover Trail Running: distance and effort-km. itra.run.
- Minetti A.E., Moia C., Roi G.S., Susta D., Ferretti G. (2002). Energy cost of walking and running at extreme uphill and downhill slopes. Journal of Applied Physiology, 93(3), 1039-1046.
What if ELYO worked it out for you?
ELYO reads your trail runs from your watch, with the distance, the elevation and your pace uphill as well as downhill, works out your training load and adjusts your plan toward your race.