Predict your race time at another distance from a recent result using the Riegel formula. Pick the distance you ran, enter your time, and choose the distance you want to predict. Free, private, and runs entirely in your browser.
The Riegel formula scales your known time by the ratio of the distances raised to the power 1.06. The exponent above 1 reflects the fact that pace slows as the distance grows.
How accurate is the Riegel formula? It works well for trained runners who have prepared for the longer distance. For a marathon, long-run training matters more than a 5K time.
Which distance should I use as input? Use a recent, all-out race at a distance close to your target for the best prediction.
A runner finishes a 5 km race in 25:00 (1,500 s). Predicted 10 km time = 1,500 × (10 ÷ 5)^1.06 ≈ 1,500 × 2.085 ≈ 3,127 s, which is 52:07, a pace of 5:13 per km.
Why 1.06? It was fitted by Pete Riegel to race records and fits most trained runners reasonably well.
Does it work for walking or cycling? No. It was built for running and the exponent would differ for other sports.
Pete Riegel, an engineer and keen runner, published a formula for predicting race times from performance at another distance in the late 1970s and early 1980s, fitting a power law to world records and personal results. The exponent of about 1.06 is still the basis for many prediction tools.
Use this calculator to set goals for your next race, to plan pacing, or to compare your results across distances. Combine it with the VO2 max calculator and the pace calculator for training. Predictions are estimates, not guarantees.
What pace should I run the first kilometer? Start at or slightly slower than your goal pace and speed up if you feel good, which avoids early fatigue.
Can I predict a time for an ultra marathon? The formula gets less reliable at very long distances, so treat any such prediction with caution.