Turn a finished marathon into 5K, 10K and half marathon equivalents
After a marathon the obvious question is what that effort is worth over shorter distances. Enter hours, minutes and seconds and you get your average pace per mile and per kilometre, your average speed, and a table of 5K, 10K and half marathon equivalents with the pace each one would need. No age grading is applied. The age-adjustment tables people quote could not be traced to an authoritative source, so rather than grade you against an unverified table this page sticks to distance conversion.
The conversion uses the Riegel distance formula, which multiplies your time by the ratio of the two distances raised to the power 1.06. That exponent is the original one. The marathon is taken as 42.195 km and the half as 21.0975 km, and miles are converted at 1,609.344 metres (as of October 2026).
The marathon is exactly where this formula struggles. Studies of race results found it tracks measured times well up to the half marathon but diverges at the marathon, and predicting a marathon from a shorter race came out at least 10 minutes too fast for half of runners. That is why this page only runs the other way, down from a marathon you actually finished. Even so the shorter distances tend to read slower than you would really race them, so use them as a starting point. Accuracy also drops below about three and a half minutes and above about four hours.
Frequently asked questions
The age-adjustment tables commonly quoted could not be traced to an authoritative source. Grading you against an unverified table would be wrong information, so only distance conversion is offered.
That is expected. The formula is known to diverge at the marathon, so coming down from a marathon tends to produce conservative short-distance equivalents.
Not reliably. In published race-result studies that direction came out at least 10 minutes too fast for half of runners, which is why this page only converts downward from a finished marathon.