Race Time Predictor
Enter a recent race or time-trial result and this race time predictor estimates your finish times for other distances using the well-known Riegel formula, from the mile to the marathon, with the pace you'll need for each.
The Pete Riegel power model predicts race time using the formula T2 = T1 × (D2 / D1)^1.06. It models aerodynamic and metabolic fatigue across race distances with exceptional accuracy for trained runners.
Format: mm:ss or hh:mm:ss (e.g. 25:00 for 5K or 1:45:00 for Half)
Predicted 10K Finish
Pace: 0:00 /km (0:00 /mi)Based on your 5K time of 25:00 using the Pete Riegel power model [T2 = T1 × (D2/D1)^1.06].
Predicted 5K
0:01
Pace: 0:00 /km
Predicted 10K
0:02
Pace: 0:00 /km
Predicted Half
0:05
Pace: 0:00 /km
Predicted Marathon
0:10
Pace: 0:00 /km
Race Time & Pacing Breakdown
| Distance | Predicted Time | Pace (/km) | Pace (/mi) | Reliability Notes |
|---|---|---|---|---|
| 1 Mile | 0:00 | 0:00 /km | 0:00 /mi | High correlation |
| 5K | 0:01 | 0:00 /km | 0:00 /mi | High correlation |
| 10K | 0:02 | 0:00 /km | 0:00 /mi | High correlation |
| Half Marathon | 0:05 | 0:00 /km | 0:00 /mi | High correlation |
| Marathon | 0:10 | 0:00 /km | 0:00 /mi | High correlation |
Formula: Pete Riegel (1981), Runner's World formula. Extrapolating beyond 3–4× input distance requires dedicated long-run mileage.
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Clinical Equations
WHO, CDC, ACSM & Mifflin-St Jeor
Suggest a Feature or Improvement for Race Time Predictor
Need custom options, higher limits, or extra format support? Let our engineering team know!
How to use Race Time Predictor
- 1Select your benchmark distance (1 Mile, 5K, 10K, Half Marathon, Marathon, or Custom).
- 2Enter your finish time in mm:ss or hh:mm:ss format.
- 3Optionally customize the fatigue factor exponent under advanced settings.
- 4View your predicted race times, necessary kilometer paces, and mile paces across all standard race distances.
How the Riegel formula works
Published in Runner's World by research engineer Pete Riegel, the 1.06 exponent reflects typical pacing decay over distance. An athlete running a 25:00 5K can expect roughly a 52:08 10K and 1:55:40 Half Marathon.
When extrapolating more than 4× the input distance (such as 5K to marathon), adequate weekly long runs and aerobic volume are required to match the predicted physiological ceiling.
Frequently Asked Questions
How accurate is the Riegel formula?
Good for similar distances; marathon predictions from short races are often too optimistic unless you've done marathon-specific training.
What is the 1.06 in the formula?
A fatigue factor: it reflects how pace slows as distance grows. Less-trained runners may slow more.
Can I predict a marathon from a 5K?
You can, but a half marathon result gives a far better marathon estimate.
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Scientific Sources & Evidence
- World Health Organization (WHO) — Body Mass Index Classification
- CDC Growth Charts — BMI-for-age LMS Percentiles
- Mifflin et al. (1990) — Basal Metabolic Rate Predictive Equations
- NICE Guideline NG246 — Identification and Management of Overweight and Obesity
- American College of Sports Medicine (ACSM) — Exercise Testing & Prescription
- European Food Safety Authority (EFSA) — Dietary Reference Values for Water