Running Pace Calculator

This running pace calculator answers the three questions every runner brings to a race plan. Pace mode takes a distance and a finish time and returns your pace per kilometer and per mile plus speed in km/h and mph — enter 5 km and 25:00 and you get 5:00 min/km, 8:03 min/mile, 12.0 km/h. Time mode works the other way: pick a distance, type the pace you can hold, and see the finish time it produces. Everything runs in your browser with no sign-up and no data sent anywhere.

Alongside the headline numbers, the tool builds a split table for your distance: a time checkpoint at every kilometer up to ten, then every fifth kilometer, then the finish line itself. Write the splits on your hand or compare them with your watch mid-race — if the 10 km mark of a two-hour half marathon reads 56:53, you know immediately whether you are ahead of or behind schedule. Standard distances (5K, 10K, half marathon 21.0975 km, marathon 42.195 km) are one click away, and a custom field accepts any distance in kilometers.

The third mode is a race-time predictor based on Peter Riegel's endurance formula T2 = T1 × (D2/D1)^1.06, the same equation used by most training-plan books. Enter one known race result — say, a recent 10K — and the tool forecasts your equivalent 5K, 10K, half-marathon and marathon times with the pace each would require. It is the fastest reality check for a goal: if the predictor puts your marathon at 4:20, a 3:45 plan is wishful thinking.

Remember that pace math describes a perfectly even race: real courses add hills, turns, weather and crowds, and Riegel's exponent assumes you are equally trained for both distances — most runners lose a little accuracy the further they extrapolate beyond a half marathon. Treat the results as a planning baseline, pace the first kilometers slightly conservatively, and update the numbers as new race results come in.