Tool · Trail
Effort-km calculator
Turn the distance and elevation gain of your trail race into an equivalent distance. The effort-km (ITRA convention) puts a number on how hard a hilly course really is and lets you compare two races with very different profiles. Add your flat-ground pace or a trail race you’ve run to estimate your finish time, fatigue and stops included.
Confidence in this estimate: low.
How this time is calculated
- Endurance pace given on flat ground: 9:39 /mi.
- Your race is 50 effort-km (distance + elevation gain/100). Time grows faster than effort (exponent 1.15), then a race factor is applied: you run faster on race day than in training, especially over short formats.
- Estimated moving time: 5 h 34.
- Estimated stops (aid stations, breaks): 18 min, i.e. 5.3% of moving time.
- Range: from 5 h 15 to 6 h 45.
- Not modeled: technical terrain, heat, altitude, night, cut-off times and descent.
- Model calibrated on 35 trail races lasting from 1 hour to about fifteen hours.
The effort-km (ITRA convention) turns a hilly course into an equivalent distance: every 100 m (328 ft) of climbing counts as one extra kilometer. Descent is not counted. Time does not grow in line with effort-km: the longer the race, the more your pace slows, and the estimate accounts for it.
How to calculate effort-km
On trails, two races of the same distance can demand very different efforts depending on their elevation. The effort-km solves that: it turns elevation into equivalent kilometers, so the whole difficulty fits into a single unit you can compare with a flat distance.
The ITRA convention
The rule used by ITRA (the International Trail Running Association) and by RunMorph is metric:
In other words, every 100 m (328 ft) of climbing adds 1 effort-km. Descent is not counted: the variant that adds elevation loss ÷ 400 is not the ITRA convention. Working in miles and feet? The calculator converts for you.
Worked example
Take an 18.6-mile (30 km) trail race with 6,560 ft (2,000 m) of climbing. The math gives 30 + 2,000 ÷ 100 = 30 + 20 = 50 effort-km, roughly the effort of about 31 flat miles, for a course that is only 18.6 miles on the map. For comparison, the UTMB (about 106 miles and 32,800 ft of climbing) comes to 171 + 10,000 ÷ 100 = 271 effort-km.
Estimating a finish time, with fatigue
Multiplying effort-km by your flat-ground pace would give 5 hours for our 50 effort-km at 9:39/mi (6:00/km). That’s too optimistic: the longer the effort, the more your pace drops. The calculator therefore makes time grow faster than effort-km (exponent 1.15), starting from your flat endurance pace scaled to a 2-hour run, then applies a race factor (you run faster on race day than in training, especially over short formats) and adds estimated stops. For our 50 effort-km, it estimates a finish around 5 h 50, with a range.
The model was calibrated on 35 real trail races lasting from 1 hour to about fifteen hours. Technical terrain, heat, altitude, night and cut-off times are not modeled: treat the result as a benchmark, to refine with your own races.
Examples of typical courses
Effort-km (distance in km + climbing in m ÷ 100) for a few common profiles, the difficulty ratio compared with the actual distance, and the estimated finish time for a runner who holds 9:39/mi (6:00/km) on the flat.
| Course | Distance | Elevation gain | Effort-km | Ratio | Est. time (9:39/mi on the flat) |
|---|---|---|---|---|---|
| Flat road 10K | 6.2 mi | 0 ft | 10 effort-km | × 1.00 | ≈ 41 min |
| Intro trail race | 9.3 mi | 1,970 ft | 21 effort-km | × 1.40 | ≈ 1 h 49 |
| Short, rolling trail | 13.0 mi | 3,280 ft | 31 effort-km | × 1.48 | ≈ 3 h 05 |
| Mountain trail | 18.6 mi | 6,560 ft | 50 effort-km | × 1.67 | ≈ 5 h 50 |
| Mid-mountain ultra | 49.7 mi | 13,120 ft | 120 effort-km | × 1.50 | ≈ 17 h 35 |
| UTMB | 106.3 mi | 32,810 ft | 271 effort-km | × 1.58 | ≈ 44 h 50 |
The ratio (effort-km ÷ distance in km) is a quick hardness gauge: close to 1, the course is runnable; above 1.6, it’s very mountainous. Times include fatigue and estimated stops; beyond 24 hours, they are ballpark figures.
Frequently asked questions
What is an effort-km in trail running?
The effort-km (or kilometer-effort) is an equivalent distance that includes a course’s elevation. The idea is that uphill, a kilometer costs far more energy than on the flat. Elevation is therefore converted into extra kilometers so you can compare the real difficulty of two courses, even with very different profiles. It’s the reference unit behind ITRA race scores.
How do I calculate effort-km?
The ITRA convention, used by RunMorph, is: effort-km = distance in km + elevation gain in meters ÷ 100. Example: 30 km (18.6 mi) with 2,000 m (6,560 ft) of climbing gives 30 + 2,000 ÷ 100 = 50 effort-km. The course takes roughly as much effort as a flat 50 km (31 mi). Some calculators add elevation loss ÷ 400: that variant is not ITRA’s, and RunMorph does not count descent.
Why is 100 m of climbing worth 1 kilometer?
It’s a field convention: on most trail climbs, gaining 100 m (328 ft) costs roughly as much as an extra flat kilometer. The ratio varies with the gradient and the runner, but this simple rule (1 km per 100 m of climbing) gives a good ballpark, easy to work out in your head and widely used by race organizers.
How do I estimate my trail finish time from effort-km?
Multiplying effort-km by your flat-ground pace underestimates the time, all the more so as the race gets longer: the longer the effort, the more your pace drops. The calculator starts from your flat endurance pace (the one you hold for 1 to 2 hours) or a trail race you’ve run, makes time grow faster than effort-km, applies a race factor and adds stops. Example: 50 effort-km with a flat pace of 6:00/km (9:39/mi) give a finish around 5 h 50, not 5 hours. Technical terrain, heat, altitude and night are not modeled.
How many effort-km is the UTMB?
The UTMB covers about 171 km (106 miles) with 10,000 m (32,800 ft) of elevation gain, so 171 + 10,000 ÷ 100 = 271 effort-km. For a runner who holds 6:00/km (9:39/mi) on the flat, the calculator estimates a finish around 45 hours, stops included, with low confidence: beyond 24 hours, any estimate stays a ballpark figure. That explains why a course like that takes dozens of hours to finish.
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