Running pace calculator

Riegel's formula and what it assumes

Peter Riegel published this in 1977 after fitting curves to race results across distances. The exponent of 1.06 encodes the fact that pace slows as distance grows — if performance scaled linearly the exponent would be 1.0.

It holds up well between about 1,500 m and the marathon for trained runners, and it is the basis of most race-time prediction tables. Two caveats: it assumes appropriate training for the target distance, and it degrades at the marathon, where fuelling, heat and muscular durability matter as much as aerobic fitness. A 10K time predicting a 3:15 marathon means the aerobic engine is capable of it, not that the day will go that way.

Even splits, and why negative splits are better

Nearly every distance world record has been set with the second half run at the same pace or faster than the first. Starting conservatively preserves glycogen and delays the accumulation of fatigue, and the time lost in the opening kilometres is generally recovered several times over later.

The opposite pattern — going out fast and fading — is the most common recreational racing error, particularly in the marathon, where the cost compounds badly over the closing 10K. A useful discipline is to run the first few kilometres at a pace that feels almost too easy.

Course and conditions change the number

• Heat. Performance falls noticeably above about 15 °C, and the effect grows with distance and humidity. Marathon times can slow by several minutes in warm conditions.
• Hills. Time lost climbing is not fully recovered descending. A rule of thumb is roughly 10 to 20 seconds per kilometre per 1% of average gradient on the way up, against less than half that gained coming down.
• Altitude. Endurance performance declines above about 1,200 m without acclimatisation.
• Wind. A headwind costs more than an equivalent tailwind returns, because drag rises with the square of relative velocity.

Pacing by effort, not just by watch

GPS pace is noisy — under trees, between buildings and on winding courses it can be several seconds per kilometre out, and chasing a fluctuating number leads to erratic running. Many experienced racers pace by perceived effort and use the watch to confirm at each kilometre marker rather than to steer continuously.

On a certified course, GPS will also usually record slightly more than the official distance, because courses are measured along the shortest legal line and almost nobody runs it exactly. Finishing pace calculated from GPS distance will therefore look marginally faster than the official result.

Common questions