Convert distance, time and pace, get your speed and see predicted race times — all in your browser.
Pace is simply time divided by distance, but it is the number every runner thinks in: 5:00 min/km says more about an effort than 12 km/h does. This calculator works in all three directions from the same equation. Give it a distance and a time and it returns your pace; give it a distance and a target pace and it returns the finishing time; give it a time and a pace and it returns how far you would go. Times are typed as h:mm:ss or mm:ss and paces as min:s, the decimal comma is understood, and every result also comes as speed in km/h and as pace per mile, using the exact conversion of 1.609344 km per mile.
Below the result the tool projects your times for 5 km, 10 km, the half marathon (21.0975 km) and the marathon (42.195 km) with the Riegel formula, T2 = T1 × (D2 ÷ D1)^1.06. Pete Riegel published it in Runner's World in 1977 after fitting race results across distances, and the exponent 1.06 encodes a simple fact: the further you go, the slower each kilometre becomes. A 10 km in 50:00, for example, projects to roughly 23:59 for 5 km, 1:50:19 for a half marathon and 3:50:01 for a marathon.
Those predictions are a reference, not a promise. The formula assumes you are equally well trained for every distance and that you can sustain the same relative effort, which is rarely true — most runners without long-run specific training finish a marathon slower than the projection, sometimes by a lot, because glycogen, muscle damage and pacing errors dominate the last ten kilometres. Heat, humidity, elevation and the course itself easily change a result by minutes, and research fitting individual runners has found exponents anywhere between about 1.06 and 1.15, with the higher values matching those who fade more on long distances. Use the table to set a plausible target and let your training runs correct it. Every calculation runs locally in your browser, with no network requests at all.
Pace = time ÷ distance; time = distance × pace; distance = time ÷ pace. Speed (km/h) = distance ÷ (time in hours). Pace per mile = pace per km × 1.609344. Riegel prediction: T2 = T1 × (D2 ÷ D1)^1.06, where T1 and D1 are the time and distance you entered.
Divide your total time by the distance: 50 minutes over 10 km gives 5:00 min/km. Type the distance and the time here and the pace, the speed in km/h and the pace per mile appear at once.
About 5:41 min/km over the 42.195 km. Enter the marathon preset and 4:00:00 as the time, leave the pace field empty, and the exact number comes out.
It is a good reference between nearby distances, such as 5 km to 10 km, and increasingly optimistic as the gap grows. Predicting a marathon from a 5 km time assumes endurance you may not have trained for, so treat the longer projections as a ceiling rather than a target.
Speed in km/h is 60 divided by your pace in minutes per kilometre: a 5:00 min/km pace is 12 km/h. The tool shows both, so you can match a treadmill setting to your outdoor pace.
Distances are entered in kilometres, but every result also shows the pace per mile, converted with the exact factor of 1.609344 km per mile. For a mile-based distance, type its value in kilometres — 5 miles is 8.04672 km.
No. Everything is calculated in JavaScript on your device, with no network requests. Nothing you type is uploaded or stored.
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