Pace vs. speed
Pace is time per unit of distance (e.g. 8:30 per mile) — what runners usually track. Speed is distance per unit of time (e.g. 7.1 mph).
Race time predictions
Predicted times use Pete Riegel's formula, which accounts for slowing down over longer distances:
Predictions are most reliable between similar distances and assume you have trained for the longer race.
Worked example
You run a 10K in 52 minutes 30 seconds. That's 3,150 seconds over 10 km, or 315 seconds per kilometer — a pace of 5:15 per km. A mile is 1.609 km, so your pace per mile is 315 × 1.609 = 507 seconds, or 8:27 per mile. Your average speed is 10 km ÷ 0.875 hours = 11.4 km/h (7.1 mph).
Pace chart: finish times at a steady pace
| Pace per mile | Pace per km | 5K | 10K | Half marathon | Marathon |
|---|---|---|---|---|---|
| 6:00 | 3:44 | 18:38 | 37:17 | 1:18:39 | 2:37:19 |
| 7:00 | 4:21 | 21:45 | 43:30 | 1:31:46 | 3:03:32 |
| 8:00 | 4:58 | 24:51 | 49:43 | 1:44:53 | 3:29:45 |
| 9:00 | 5:36 | 27:58 | 55:55 | 1:57:59 | 3:55:58 |
| 10:00 | 6:13 | 31:04 | 1:02:08 | 2:11:06 | 4:22:11 |
| 11:00 | 6:50 | 34:11 | 1:08:21 | 2:24:12 | 4:48:24 |
| 12:00 | 7:27 | 37:17 | 1:14:34 | 2:37:19 | 5:14:38 |
This table assumes you hold exactly the same pace for the whole distance. The calculator's race predictions are different: they allow for the fact that most runners slow down as the distance gets longer.
Race distances
- 5K = 3.11 miles
- 10K = 6.21 miles
- Half marathon = 13.1 miles (21.0975 km)
- Marathon = 26.2 miles (42.195 km)
Frequently asked questions
What's a good running pace?
It depends entirely on your age, experience and the distance. Many recreational runners complete a 5K at somewhere between 9 and 12 minutes per mile. The most useful comparison is with your own previous runs.
How do I run a 5K in under 30 minutes?
You need to average faster than 9:39 per mile, or 6:00 per kilometer. A common approach is to practice short intervals at that goal pace with easy jogging in between, gradually lengthening the intervals.
What are negative splits?
Running the second half of a race faster than the first. Starting slightly slower than your target pace and speeding up later is usually more efficient than starting fast and fading.
How accurate are the race predictions?
They're most reliable between similar distances — a 10K time predicts a half marathon well — and they assume you've trained for the longer distance. Predicting a marathon from a 5K tends to be optimistic, because endurance becomes the limiting factor.