Tool · Trail
Effort-km calculator
Turn the distance and elevation gain of your trail race into an equivalent distance on flat ground. The effort-km (ITRA formula) puts a number on how hard a hilly course really is and lets you compare two races with very different profiles. Add your reference pace to estimate your finish time.
The effort-km (ITRA formula) turns a hilly course into an equivalent distance on flat ground: every 100 m (328 ft) of climbing counts as one extra kilometer, and so does every 400 m (1,312 ft) of descent. The estimated time assumes you hold your reference pace on every effort-km: it’s a ballpark figure; technical terrain, heat and fatigue come on top.
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 formula
The most widely used rule, adopted by ITRA (the International Trail Running Association), is metric:
In other words, every 100 m (328 ft) of climbing adds 1 effort-km, and every 400 m (1,312 ft) of descent adds 1 effort-km too (downhills take their toll as well, especially on your quads). 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 (ignoring the descent). The math gives 30 + 2,000 ÷ 100 = 30 + 20 = 50 effort-km, the equivalent 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
If you know your reference pace on flat ground, you can estimate your time: time = effort-km × reference pace per km. For our 50 effort-km at 9:39/mi (6:00/km), that’s about 5 hours. It’s a ballpark figure: technical terrain, heat, altitude and fatigue often stretch that time.
Sample courses
Effort-km calculated with the ITRA formula (distance in km + climbing in m ÷ 100) for a few common profiles, and the difficulty ratio compared with the actual distance.
| Course | Distance | Elevation gain | Effort-km | Ratio |
|---|---|---|---|---|
| Flat road 10K | 6.2 mi | 0 ft | 10 effort-km | × 1.00 |
| Intro trail race | 9.3 mi | 1,970 ft | 21 effort-km | × 1.40 |
| Short, rolling trail | 13.0 mi | 3,280 ft | 31 effort-km | × 1.48 |
| Mountain trail | 18.6 mi | 6,560 ft | 50 effort-km | × 1.67 |
| Mid-mountain ultra | 49.7 mi | 13,120 ft | 120 effort-km | × 1.50 |
| UTMB | 106.3 mi | 32,810 ft | 271 effort-km | × 1.58 |
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. To account for descents, add elevation loss in meters ÷ 400 to these values.
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 most common formula, ITRA’s, is: effort-km = distance in km + elevation gain in meters ÷ 100. Elevation loss ÷ 400 is sometimes added too, since downhills also tire you out. 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 as much effort as a flat 50 km (31 mi).
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?
Multiply your effort-km by your reference pace per kilometer on flat ground. Example: 50 effort-km at 6:00/km (9:39/mi) gives about 5 hours. It’s a first estimate: out on the course, technical terrain, heat, altitude, aid stations and fatigue often stretch that time. Best to calibrate it against your own past races.
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. With the simple ITRA formula, that’s 171 + 10,000 ÷ 100 = 271 effort-km, the equivalent of a 271 km (168-mile) race on flat ground. That explains why a course like that takes dozens of hours to finish.
Train for your trail race with a plan built for the climbing
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