Run 10 km in 50:00 and your pace is 5:00 per kilometre, or 8:03 per mile
Pace is the time it takes to cover one mile or one kilometre. Divide the time by the distance: 10 km in 50:00 is 3,000 seconds ÷ 10 = 300 seconds, so 5:00/km. That is 12.0 km/h (7.46 mph) and 8:03 per mile. Hold the same pace over a half marathon (21.0975 km) and you finish in 1:45:29; over a marathon (42.195 km), in 3:30:59.
In practice, the longer the race, the harder it is to hold the same pace. So the calculator above shows the even-pace time next to a Riegel prediction, which allows for slowing down as distance grows (a 10 km in 50:00 predicts a half marathon of about 1:50:19), and draws both as a distance-versus-time curve.
How the calculation works
- Choose what to solve for. Pick pace (enter distance and time), finish time (enter distance and pace) or distance (enter time and pace). Everything is converted to seconds first.
- Three formulas. Pace = time ÷ distance, finish time = distance × pace, and distance = time ÷ pace. Speed is the same relationship turned upside down: distance ÷ time, shown in mph or km/h.
- Miles. One mile is converted at the defined value of 1.609344 km. If you switch units without editing a field, the result is calculated from the value you first typed, so no rounding error creeps in.
- Track laps. A standard track is 400 m, so a lap takes the per-kilometre pace × 0.4. At 5:00/km that is 2:00 for 400 m and 1:00 for 200 m.
- Standard distances. 5K, 10K, half marathon (21.0975 km) and marathon (42.195 km) times are worked out both at an even pace and with the Riegel prediction. The splits table gives the elapsed time at every mile or kilometre (every 5 for long distances, plus the half marathon point).
Race times at common paces
| Pace (/mile) | 5K | 10K | Half marathon | Marathon | Speed | Pace per km |
|---|---|---|---|---|---|---|
| 6:00 | 18:38 | 37:17 | 1:18:39 | 2:37:19 | 10.00 mph | 3:44 |
| 7:00 | 21:45 | 43:30 | 1:31:46 | 3:03:32 | 8.57 mph | 4:21 |
| 8:00 | 24:51 | 49:43 | 1:44:53 | 3:29:45 | 7.50 mph | 4:58 |
| 9:00 | 27:58 | 55:55 | 1:57:59 | 3:55:58 | 6.67 mph | 5:36 |
| 10:00 | 31:04 | 1:02:08 | 2:11:06 | 4:22:11 | 6.00 mph | 6:13 |
| 11:00 | 34:11 | 1:08:21 | 2:24:12 | 4:48:24 | 5.45 mph | 6:50 |
| 12:00 | 37:17 | 1:14:34 | 2:37:19 | 5:14:38 | 5.00 mph | 7:27 |
Times are rounded to the second. To break 4 hours in the marathon you need to average 5:41/km (3:59:48) or faster, which is about 9:09 per mile. At 5:42/km the finish is 4:00:31, just over the line.
Predicting other distances: the Riegel formula and its limits
In 1981 Peter Riegel showed that, for endurance events such as running, swimming and cycling, times between about 3.5 and 230 minutes follow a relationship of the form time = a × distanceb. From one result T₁ at distance D₁ you can estimate the time at another distance D₂ as T₂ = T₁ × (D₂ ÷ D₁)b. The calculator uses the commonly applied b = 1.06. In Riegel's paper the running exponent was 1.077 for men and 1.083 for women using world records, and 1.05 to 1.06 for men aged 40 to 70.
| 10K time | Half marathon prediction | Marathon prediction | Marathon predicted pace |
|---|---|---|---|
| 40:00 | 1:28:15 | 3:04:00 | 7:01/mi |
| 45:00 | 1:39:17 | 3:27:01 | 7:54/mi |
| 50:00 | 1:50:19 | 3:50:01 | 8:46/mi |
| 55:00 | 2:01:21 | 4:13:01 | 9:39/mi |
| 1:00:00 | 2:12:23 | 4:36:01 | 10:32/mi |
| 1:10:00 | 2:34:27 | 5:22:01 | 12:17/mi |
A study of 2,303 recreational runners (Vickers and Vertosick, 2016) found that the Riegel formula worked well up to the half marathon but predicted marathon times that were much too fast: for half of the runners, at least 10 minutes faster than they actually ran. Read a marathon prediction as an optimistic estimate, and if it is your first marathon, start slower than the predicted pace. If your reference time is shorter than 3 minutes 30 seconds or longer than 3 hours 50 minutes (230 minutes), the calculator shows no prediction.
Using the result in training
- Know where you stand. If you ran a recent 10K in 50:00, 5:00/km is your baseline. Set the next 10K goal a few seconds per kilometre faster.
- Goal time to pace. Choose finish time, enter a distance and a target pace, and see whether the goal is realistic. A half marathon at 9:00/mi comes to 1:57:59. For a first half, start a little more comfortably than that.
- Set time to distance. Choose distance and enter 60 minutes at 8:00/mi: that is 7.5 miles.
- Race day. Compare your watch with the splits table at the 5 mile or 5 km mark and the half marathon point, and you will see at once if you went out too fast. For track sessions, use the 400 m lap time.
Common mistakes
- Mixing up pace and speed. Pace is minutes per mile or kilometre, so a smaller number is faster. Speed is miles or kilometres per hour, so a bigger number is faster. 8:00/mi is 7.5 mph, and 5:00/km is 12.0 km/h.
- Treating minutes as decimals. 8.5 minutes is 8:30, not 8:50. The calculator takes minutes and seconds in separate boxes.
- Using 26 miles for the marathon or 21 km for the half. The marathon is 42.195 km (26.2188 miles) and the half is 21.0975 km. At 10:00/mi, 26 miles gives 4:20:00, while the full marathon distance takes 4:22:11, 2 minutes 11 seconds more.
- Entering miles in the kilometre field. If a race or watch reports miles, switch the unit to miles first so the pace and distance match.
- Stretching a short-race pace over a long distance. Your 10K pace usually fades badly over a marathon. Compare the even-pace and prediction columns in the standard-distance table.
Limits and safety
- The calculation assumes the average pace holds all the way. Hills, wind, heat, aid stations, traffic lights and GPS distance error on your watch can all change your splits.
- Track, road and trail feel different even at the same pace.
- The Riegel prediction is a rough estimate that assumes you have prepared equally well for each distance, and it tends to come out too fast for the marathon.
- If you feel pain, dizziness or unusual breathlessness, stop and look after your body before worrying about the time.
Basis date The standard distances, the mile conversion, the Riegel exponent and its range of use, and the prediction-accuracy study in this article were checked against the original sources on 2026-10-08.
Sources
- 01Riegel PS. Athletic Records and Human Endurance. American Scientist 69(3):285–290, 1981Straight-line time–distance relationship for about 3.5 to 230 minutes; Table 1 running exponent 1.07732 for men and 1.08283 for women, 1.05 to 1.06 for men aged 40 to 70
- 02Vickers AJ, Vertosick EA. An empirical study of race times in recreational endurance runners. BMC Sports Sci Med Rehabil 20162,303 recreational runners; the Riegel formula fit well up to the half marathon but predicted marathon times at least 10 minutes too fast for half of the runners
- 03World Athletics: Course Measurement Book 2023Half marathon 21.0975 km, marathon 42.195 km
- 04World Athletics: Technical RulesStandard track length 400 m, standard road distances
- 05NIST: Revised Unit Conversion Factors1 mile = 1,609.344 m
Frequently asked questions
How do I calculate running pace?
Convert your time to seconds and divide by the distance. A 10 km run in 50:00 (3,000 seconds) is 3,000 ÷ 10 = 300 seconds, or 5:00 per kilometre. In the calculator, choose pace as the value to solve for and enter the distance and time.
What is the difference between pace and speed?
Pace is the time it takes to cover one mile or kilometre, so a smaller number is faster. Speed is the distance covered in an hour, so a bigger number is faster. A pace of 5:00/km is a speed of 12.0 km/h.
What distances does the calculator use for the half marathon and marathon?
The official World Athletics distances: 21.0975 km for the half marathon and 42.195 km for the marathon. At 5:00/km that gives 1:45:29 and 3:30:59. The 5K and 10K are 5 km and 10 km.
Can I predict my half marathon or marathon time from a 10K?
You can estimate it with the Riegel formula (predicted time = time × (target distance ÷ distance run)^1.06). A 10K in 50:00 predicts about 1:50:19 for the half marathon and 3:50:01 for the marathon. A study of 2,303 recreational runners found the formula fit well up to the half marathon but predicted marathon times at least 10 minutes too fast for half of the runners.
Can I enter miles and still see kilometre results?
Yes. Switch the distance unit to miles and enter the distance and pace in miles; the results show pace per km and per mile, and speed in km/h and mph. One mile is converted at the defined value of 1.609344 km.
What pace do I need to run a marathon in under 4 hours?
You need to average 5:41/km or faster over 42.195 km. 5:41/km gives 3:59:48, while 5:42/km gives 4:00:31. In miles, that is about 9:09 per mile.
How fast should I run a lap of the track?
A standard track lap is 400 m, so multiply your per-kilometre pace by 0.4. At 5:00/km, 400 m takes 2:00 and 200 m takes 1:00; at 4:30/km, 400 m takes 1:48.
Is average pace enough to plan a race?
Average pace is a baseline for hitting a goal time. In a real race, hills, aid stations, weather and early excitement all move your pace, so use the 5-mile (or 5 km) and half marathon points in the splits table to check you did not go out too fast, and start slower than the prediction column over long distances.