Racing
Race time predictor
Enter a PB and get an estimate for every track event from 60 m to 10,000 m. The estimates come from the Riegel formula. Enter two PBs and it works out your own exponent.
How it is calculated
The predictor uses the formula Peter Riegel published in 1981. It says your time grows a little faster than the distance.
T1 is your PB time over distance D1. T2 is the estimate for distance D2. Riegel fitted k = 1.06 to world records. With 1.06, your pace slows by about 4% each time the distance doubles.
In two PBs mode, the predictor works out the exponent that fits both of your PBs:
It then uses that exponent for every other event. Your two PBs stay exactly as you entered them.
This page uses one formula. It is not the race prediction in the StrideBuddy app, which reads your training diary.
Worked example
A runner has a 1500 m PB of 4:10.00. For 5000 m the formula gives 250 s × (5000 ÷ 1500)1.06 = 895.8 s, which is 14:55.8. That is 71.7 s per 400 m, against 66.7 s per 400 m in the 1500 m.
The same runner also has an 800 m PB of 2:00.00. In two PBs mode the exponent becomes ln(250 ÷ 120) ÷ ln(1500 ÷ 800) = 1.168. That runner slows more than average as the race gets longer, so the 5000 m estimate goes up.
Limits
- The formula comes from world records over longer races. It does not describe sprints well, so every estimate below 400 m, or made from a sprint PB, is marked rough.
- The further the race is from your PB, the bigger the error. Estimates more than 4 times longer or shorter than your nearest PB are marked rough.
- It assumes you train for the target race. A 1500 m runner who never runs long will not run the predicted 10,000 m.
- It knows nothing about the weather, the race tactics or how fit you are today.
Sources
Riegel, P. S. (1981). Athletic records and human endurance. American Scientist, 69(3), 285–290. jstor.org/stable/27850427
Questions
How does the Riegel formula work?
It assumes your time grows a little faster than the distance. The formula is T2 = T1 × (D2 ÷ D1)^1.06. Each time the distance doubles, your pace slows by about 4%.
How accurate is the race time predictor?
It is a formula, not a test of your fitness. It is closest when the race is near the distance of your PB and you train for that race. It is least reliable for sprints and for races much longer or shorter than your PB.
Which exponent should I use?
1.06 is Riegel's value and a fair start. If you have two recent PBs, use the two PBs mode to work out your own. A lower exponent means you hold your pace well in longer races. A higher one means you are stronger over shorter races.
Is this how StrideBuddy predicts race times?
No. This page uses one formula. The StrideBuddy app uses AI to read your training diary and predict your race times. Each prediction shows the most likely time, a range around it and a confidence level.
Race predictions from your training.
StrideBuddy is a training diary for track athletes. It uses AI to read your diary and predict your race times, with the most likely time, a range around it and a confidence level.