Race Time Predictor Between Distances
Enter a reference time and a distance, and discover your theoretical times on other distances (5k, 10k, half-marathon, marathon...). This calculation is based on Riegel's formula, widely used in performance calculators.
The calculator takes into account the runner's profile (beginner, regular, well-trained) to adjust predictions: an experienced runner maintains pace better over longer distances, while a beginner slows down more as the distance increases.
Estimated equivalent times
| Distance | Predicted time | Average pace |
|---|---|---|
| Enter your time and click "Calculate equivalences" to see predictions. | ||
Example prediction: 10K in 50:00 (regular runner)
| Distance | Predicted time | Average pace | Speed |
|---|---|---|---|
| 1500 m | 6:42 | 7:12/mi | 8.3 mph |
| 3K | 13:57 | 7:29/mi | 8.0 mph |
| 5K | 24:00 | 7:44/mi | 7.8 mph |
| 10K | 50:00 (ref.) | 8:03/mi | 7.5 mph |
| 15K | 1:16:52 | 8:15/mi | 7.3 mph |
| Half-marathon | 1:50:23 | 8:26/mi | 7.1 mph |
| Marathon | 3:49:53 | 8:47/mi | 6.8 mph |
Runner profile impact on race time (ref. 10K in 50:00)
| Distance | Beginner (k=1.08) | Regular (k=1.06) | Highly trained (k=1.04) |
|---|---|---|---|
| 5K | 23:39 | 24:00 | 24:19 |
| 10K | 50:00 (same reference) | ||
| Half-marathon | 1:52:03 | 1:50:23 | 1:48:40 |
| Marathon | 3:56:47 | 3:49:53 | 3:43:28 |
On shorter distances, a beginner is predicted faster because they slow down more over long distances: their "pure" speed is therefore higher than a trained runner with the same 10K time.
Frequently asked questions about race time prediction
How does Riegel's formula predict race times?
The formula T2 = T1 × (D2/D1)k relates a reference time T1 over distance D1 to a predicted time T2 over distance D2. The exponent k (between 1.04 and 1.08) models the performance drop-off as distance increases. A higher k means greater slowdown.
How accurate is the race time prediction?
The formula is reliable for efforts between 3.5 minutes and 4 hours, provided you are trained for the target distance. It becomes less accurate for very large gaps (e.g. predicting an ultra from a 1500 m) or without specific preparation.
How do I choose the right runner profile?
Beginner (k=1.08): less than 2 years of running or limited long-distance experience. Regular (k=1.06): 3–4 sessions per week with some race experience. Highly trained (k=1.04): competitive runner with high training volume and multiple marathons.
Can I predict a marathon time from a 10K?
Yes, this is one of the most common uses. From a 50-minute 10K (regular profile), the formula predicts about 1:50 for a half-marathon and 3:50 for a marathon. However, specific preparation (long runs, nutrition, race management) is crucial.
How can I improve my predicted time?
Work on your VO2max with interval training, include long runs for endurance, and practice race-pace sessions. Optimizing racing weight, shoe choice, and managing race-day temperature can also make a difference.
About Riegel's formula
Estimates are based on Riegel's formula, used by many performance
calculators (race predictors). It links a reference time T1 on a distance D1
to a predicted time T2 on a distance D2:
- Valid mainly for efforts between 3.5 minutes and 4 hours.
- Assumes you are trained for the target distance (a 10k doesn't predict a 100k!).
- The further the target distance from your reference distance, the more approximate the result.
To further refine your forecasts, you can also check your VO₂ max, calculate your specific training paces and adjust your plan according to your heart rate. Don't forget that temperature and your choice of shoes can also impact your race time.
Who was Peter "Pete" Riegel?
- American mechanical engineer (1935–2018) passionate about distance running.
- Specialist in official road course measurement and active volunteer in the running community.
- Author in 1977, in Runner's World, of the simple formula that predicts time on another distance: the famous Riegel curve.