What pace you are running
Running pace is time divided by distance: pace = minutes ÷ kilometres. Running 10 km in 55 minutes gives 5.5 min/km, read as 5:30 per kilometre, and equals 10.9 km/h. From one honest performance any other distance can be projected with Riegel's formula, time₂ = time₁ × (distance₂ ÷ distance₁) raised to 1.06: the same 10 km in 55 minutes projects a half marathon of 2 h 1 min.
The formula
Pace (min/km) = Time in minutes ÷ Distance in km · Speed (km/h) = Distance ÷ (Time ÷ 60) · Riegel projection: Time₂ = Time₁ × (Distance₂ ÷ Distance₁)^1.06. The 1.06 exponent is the one Peter Riegel fitted on real race results, and it expresses that pace decays slightly as distance grows.
What each variable means
- Distance
- The distance actually covered, in kilometres. A watch GPS can drift 1 to 2% in a city, and that error passes straight into the pace.
- Total time
- Minutes on the clock, start to finish. If you stopped at traffic lights, the pace here is the real one for the outing, not the pace of the running segments.
Precomputed values
| 10 km in | Pace | Speed | Half marathon | Marathon |
|---|---|---|---|---|
| 40 min | 4:00 /km | 15,0 km/h | 1h 28 | 3h 04 |
| 45 min | 4:30 /km | 13,3 km/h | 1h 39 | 3h 27 |
| 50 min | 5:00 /km | 12,0 km/h | 1h 50 | 3h 50 |
| 55 min | 5:30 /km | 10,9 km/h | 2h 01 | 4h 13 |
| 60 min | 6:00 /km | 10,0 km/h | 2h 12 | 4h 36 |
| 70 min | 7:00 /km | 8,6 km/h | 2h 34 | 5h 22 |
Each row projects with Riegel from the 10 km mark. The useful reading is the distance between columns: taking 5 minutes off a 10 km moves the projected marathon by almost 25, because the error multiplies with distance. That is why short-distance marks are used to calibrate training rather than to promise a marathon time.
Run it on your numbers
How to read the result
Pace comes out in decimal minutes: 5.5 min/km is 5 minutes 30 seconds, and the second reading in the result gives you those seconds already converted. The half and marathon projections assume you trained for that distance; without the weekly volume behind it, the real time lands above the estimate.
Assumptions and limits
- Pace is an average, not an instantaneous reading. An outing with 2 km of climb and 8 flat collapses into a number that describes no segment of it.
- Riegel's projection was fitted on runners trained for the target distance. Extrapolating from 5 km to a marathon with no volume base always overestimates.
- The 1.06 exponent is a population average: runners with a deep aerobic base lose less, and fast but distance-untrained runners lose more.
- Heat, wind, altitude and elevation gain enter neither formula.
