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5K race predictor

What could you run for 5K right now? The Riegel formula projects it from any recent race, so one 10K or half marathon result sets a realistic 5K goal and pace.

5K race predictor

Riegel formula from any recent race.

Predicted 5K time
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Enter a recent race distance and time.

Predicted pace
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Riegel exponent
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Riegel formula: T2 = T1 x (D2 / D1)^1.06. Works best when the recent race is within the last 6 weeks.
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The Riegel formula

Exercise physiologist Peter Riegel found that race times scale with distance to the power of 1.06: T2 = T1 x (D2/D1)^1.06. It captures how endurance fades with distance better than simple proportional scaling.

Getting a trustworthy prediction

Use a recent all-out race within 6 weeks, on a similar course profile. Predictions stretch well across neighboring distances but get optimistic for marathon jumps from short races.

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Race Predictor 5K FAQs

How does the Riegel formula work?
It scales your known time by the distance ratio raised to 1.06. A 50:00 10K predicts 50:00 x (5/10)^1.06, about 24:00 for 5K.
How accurate are 5K predictions?
Usually within 30 to 60 seconds when the input race is recent and maximal. Heat, hills, and poor pacing in the input race all distort the output.
Can I predict 5K from a marathon time?
Roughly, but the formula gets optimistic across big jumps. A recent 10K or a hard 5K time trial predicts 5K far better.
What pace should I target in the 5K?
The predicted pace per kilometer is shown in the results. Start a touch conservatively and build; most runners go out too hard.
Does Riegel work for beginners?
Less well. Beginners improve fast and pace unevenly, so predictions from one race to the next often undersell what is possible.
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