Running pace calculator
Convert between pace, speed and finish time: enter a distance and a time to get per-kilometre and per-mile pace, km/h and mph, plus even-pace splits, with finish times projected by the Riegel formula (Riegel, American Scientist 1981), T₂ = T₁ × (D₂/D₁)^1.06, and 1 mile = 1609.344 m.
Runs in your browserEvery computation happens in your browser — your data never leaves this device.
Distance and time
Pace assumes an even effort; splits are just that average divided up, and real races drift between halves.
Result
Enter a distance and a time, then press “Calculate pace”.
What this tool does
- Turn a finished 10 km into a pace so you can tell whether it counted as an easy run or a threshold session.
- Plan race splits: for a 1:45 half marathon, work out the 4:59/km even pace first, then decide how much to hold back over the first 5 km.
- Convert a treadmill mph readout into minutes per kilometre without doing the arithmetic in your head mid-run.
- Project a half or full marathon from a recent 5 km or 10 km (Riegel formula) and set a realistic target pace.
Example
Input
Distance 10 km, time 50:00
Output
Pace 5:00/km, 8:03/mi, speed 12.00 km/h (7.46 mph); 10 one-kilometre splits of 5:00 each
From a recent 5 km in 25:00, Riegel projects 10 km at 52:07 (1500 × 2^1.06 seconds).
Frequently asked questions
What is the difference between pace and speed?
They are reciprocals: pace is the time per kilometre, speed is the distance per hour. Runners prefer pace because splits are easy mental arithmetic, cyclists prefer speed. This tool reports both.
What does the 1.06 in the Riegel formula mean?
Riegel (1981) found that race times scale with distance as a power law with an exponent near 1.06: T₂ = T₁ × (D₂/D₁)^1.06. It assumes your endurance base stays the same, so long extrapolations — a marathon from a 10 km — run optimistic, typically 2–5 minutes faster than reality.
Why is per-mile pace not just per-km pace times 1.6?
That is a decent approximation; the exact factor is 1.609344. So 5:00/km becomes 8:03/mi. This tool converts with the exact 1609.344 m mile, which is why it drifts a few seconds from the rough multiplication.
Are the splits useful?
Useful but limited: they divide the average evenly and say nothing about crowds, hills or aid stations. Their value is giving you a baseline for what you should be running, and most racers should go slightly slower than average early on.
How do I handle a treadmill readout?
Treadmills show mph or km/h. Either switch the unit to miles and enter the distance, or compare the speed readout against the km/h figure here. No network access is involved.
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