Race time prediction calculator
Peter Riegel's formula scales times by distance to the power 1.06. It is remarkably good between about 5K and the marathon.
Predicted time
1:39:17
- Predicted pace per km
- 4:42
- Your current pace per km
- 4:30
- Slowdown per kilometre
- 4.58 %
- What a linear scaling would predict
- 1:34:56
- How much slower than linear
- 0:04:21
Show the working
- Distance you have raced = 10
- Your time, hours = 0
- Minutes = 45
- Seconds = 0
- Target distance = 21.0975
- Fatigue exponent = 1.06
- known_seconds_total = 0*3600 + 45*60 + 0 = 2700
- ratio = 21.0975 / 10 = 2.109 75
- Predicted time = 2700 * 2.109 75^1.06 = 5957.29
- Predicted pace per km = 21.0975 > 0 ? 5957.29 / 21.0975 : 0 = 282.369
- Your current pace per km = 10 > 0 ? 2700 / 10 : 0 = 270
- Slowdown per kilometre = 270 > 0 ? (282.369/270 - 1) * 100 : 0 = 4.581 26
- What a linear scaling would predict = 2700 * 2.109 75 = 5696.33
- How much slower than linear = 5957.29 - 5696.33 = 260.963
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- T2 = T1 x (D2 / D1)^1.06
The exponent 1.06 was fitted to race results and works best from 3 km to 42 km. Ultras need a larger exponent.
A prediction assumes you have trained for the target distance. Riegel does not know whether you have run 30 km before.