Race time predictor
Enter a distance you have recently raced flat out and the time you achieved. The prediction uses Riegel's formula with an exponent of 1.06.
The formula assumes training appropriate to the predicted distance. A good 5 km does not deliver the predicted marathon if you have never run past 20 kilometres — the marathon prediction is the most optimistic of the set.
Frequently asked questions
How accurate is Riegel's formula?
Good between 5 and 21 kilometres, optimistic for the marathon. Peter Riegel published it in 1977 and 1.06 is the exponent he found across race data.
Which distance gives the best prediction?
The one closest to your target. For a marathon, a recent half marathon predicts far better than a 5 km.
Why is the predicted marathon too fast?
Because the formula does not model glycogen depletion, which hits around 30 kilometres and has no equivalent over short distances.