Predict 10K Time from a 20-Minute 5K
A 20-minute 5K predicts a 10K finish time of approximately 41 minutes 39 seconds.
How to use this tool
- Enter known distance, known time — minutes, known time — seconds and target distance in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your predicted minutes and the full breakdown beneath it.
Estimate your 10K race time based on your 20-minute 5K personal best.
Frequently asked questions
- What is the Riegel formula?
- T2 = T1 × (D2 / D1)^1.06, where T1 is your known time over distance D1, T2 is the predicted time over target distance D2. The exponent 1.06 reflects the fact that runners slow slightly at longer distances.
- How accurate is the Riegel predictor?
- It is most accurate within a factor of ~2–3× of the known distance. Predicting a marathon from a 10 km is reasonable; from a 400 m sprint, much less so. Terrain, weather, and fitness level all affect actual results.