Pace, time and distance
Pace is time per unit of distance — the way runners think — while speed is distance per unit of time. Knowing any two of distance, time and pace gives you the third. The calculator works in seconds and kilometers internally and converts with the exact international mile (1 mile = 1.609344 km), then rounds the displayed times to the nearest second.
The formulas
Pace = time / distance Time = distance × pace Distance = time / pace Speed (mph) = 3600 / pace in seconds per mile 1 mile = 1.609344 km
Worked examples
A 10K in 52:30: 3,150 seconds / 10 km = 315 s = 5:15 per km. In miles, 10 km = 6.2137 mi, so 3,150 / 6.2137 = 507 s = 8:27 per mile, a speed of 7.10 mph (11.43 km/h).
A marathon at 9:00 per mile: 26.219 mi × 540 s = 14,158 s = 3:55:58.
Limitations
- Assumes an even pace. Hills, wind, heat and fatigue mean real splits vary; most runners slow in the second half of a marathon.
- A pace you can hold for 5K does not scale linearly to longer races. Use a recent race at a similar distance to set goals.
Sources: World Athletics, Competition and Technical Rules (road race distances, course measurement); NIST, Unit conversion factors (1 mile = 1.609344 km).
Frequently asked questions
How long is a half marathon and a marathon?
A marathon is 42.195 km (26.219 miles) and a half marathon 21.0975 km (13.109 miles), the distances set by World Athletics. A 5K is 3.107 miles and a 10K 6.214 miles. Pick a race from the list to fill the distance exactly.
How do I convert pace per mile to pace per kilometer?
Divide the per-mile pace by 1.609344. A 9:00 per mile pace is 540 / 1.609344 = 335.5 seconds, or 5:36 per kilometer. To go the other way, multiply by 1.609344.
What pace do I need for a sub-4-hour marathon?
4:00:00 over 26.219 miles is 9:09 per mile (5:41 per km). Choose "Pace", pick Marathon, enter 4:00:00 and the calculator shows it, along with the split at every mile or kilometer.
Why doesn't my watch agree with the race distance?
GPS tends to measure courses slightly long because you rarely run the exact measured line, and signal drift adds distance. Certified courses are measured along the shortest legal route, so your watch may show 26.4–26.5 miles for a marathon.
How should I enter times?
Use hours:minutes:seconds, such as 1:52:30, or minutes:seconds, such as 52:30. A single number is read as seconds.
This calculator is for general information and screening only and is not medical advice. Talk to a doctor or registered dietitian before making changes based on the result, especially if you are pregnant, under 18, or managing a health condition.