How to use it
- Choose miles or kilometers.
- Pick what to calculate: pace, finish time or distance.
- Enter the two values you know, or tap a race distance.
- Read your pace, time, speed and race predictions.
Pace, time and distance
Pace, time and distance are linked by one simple equation, so if you know two you can find the third:
- Pace = time ÷ distance
- Time = pace × distance
- Distance = time ÷ pace
Enter times as h:mm:ss or mm:ss (for example 55:00 or 1:52:30) and paces as mm:ss per mile or per km. The calculator also shows your speed in mph or km/h and your pace in the other unit.
Worked examples
- Pace: 6.2 miles (10K) in 55:00 → 55 ÷ 6.2 ≈ 8:52 per mile (5:30 per km), about 6.8 mph.
- Finish time: a half marathon (13.1 mi) at 9:00 per mile → 9 × 13.1 = 117.9 minutes ≈ 1:57:54.
- Distance: 45 minutes at 10:00 per mile → 4.5 miles.
Tap 5K, 10K, Half marathon or Marathon to fill in the exact race distance.
Race time predictions
Below your result, the calculator predicts times at other distances with the Riegel formula:
T₂ = T₁ × (D₂ ÷ D₁)^1.06
The exponent 1.06 reflects that you slow down slightly as the distance grows. For example, a 25:00 5K predicts about 52:07 for 10K and about 1:55 for a half marathon.
The prediction assumes you've trained for the longer distance. For the marathon in particular it's usually optimistic for recreational runners, because fueling, pacing and endurance matter more as the race gets longer.
Pace chart for common race times
| Goal | 5K | 10K | Half marathon | Marathon |
|---|---|---|---|---|
| 8:00 per mile | 24:51 | 49:42 | 1:44:53 | 3:29:45 |
| 9:00 per mile | 27:58 | 55:55 | 1:57:59 | 3:55:58 |
| 10:00 per mile | 31:04 | 1:02:08 | 2:11:06 | 4:22:11 |
| 11:00 per mile | 34:11 | 1:08:21 | 2:24:12 | 4:48:24 |
Pacing tips
- Start conservatively. Running the first mile 10–20 seconds slower than goal pace often leads to a faster finish.
- Train by effort, not just pace. Heat, hills and wind slow you down; the target heart rate calculator helps you keep easy runs easy.
- Use the predictions to set realistic goals, then adjust after a tune-up race.
- Convert treadmill speeds: 6 mph is a 10:00 mile, 7 mph about 8:34, 8 mph 7:30.
All calculations run in your browser.
Frequently asked questions
How do I calculate my running pace?
Divide your total time by the distance. For example, 30 minutes for 3 miles is a 10:00 per mile pace.
What is a good 5K time?
It depends on age, sex and experience. Many recreational runners finish between about 25 and 35 minutes.
How accurate is the Riegel race predictor?
It works well for trained runners between similar distances. Marathon predictions from short races are often too optimistic.
How do I convert pace per km to pace per mile?
Multiply the pace per km by 1.609. A 5:30 per km pace is about 8:51 per mile.
How long is a half marathon?
13.1 miles (21.0975 km). A marathon is 26.2 miles (42.195 km).
Sources
- Riegel PS: Athletic records and human endurance. Am Sci 1981 (PubMed)
- Vickers AJ, Vertosick EA: An empirical study of race times in recreational endurance runners. BMC Sports Sci Med Rehabil 2016 (PubMed)
- Physical Activity Guidelines for Americans (health.gov)
Last reviewed: November 14, 2026 · Kitpebble editorial team
Change log
- : Sources expanded; FAQ and content reviewed.
For general information only; not medical advice or a diagnosis. How we write and review our pages