How this calculator works
Pick what you want to solve for — pace, finish time, or distance — and enter the other two. Distance can be a common race (5K, 10K, half marathon, marathon) or a custom value in kilometers or miles. Pace is always shown in both per-kilometer and per-mile form so you do not need to convert by hand.
Splits and pace calculations are exact once you fix the distance definition: this calculator uses the standard race distances (5 km, 10 km, 21.0975 km, 42.195 km) and the exact international mile of 1.609344 km, so conversions between km and mile pace are consistent to the second.
The formulas
Pace = total time ÷ distanceTime = pace × distanceDistance = total time ÷ paceMile pace from km pace: seconds per mile = seconds per km × 1.6093441 mile = 1.609344 km exactly (the international mile), so pace-per-mile is always derived from pace-per-km using this fixed factor rather than a rounded approximation.
Worked example: 5K in 25:00
- Total time is 25:00 = 1,500 seconds over a 5 km distance.
- Pace per km: 1,500 seconds ÷ 5 km = 300 seconds/km = 5:00 per km.
- Pace per mile: 300 × 1.609344 = 482.8 seconds/mi ≈ 8:03 per mile.
- Running the same pace over a marathon (42.195 km) would finish in 42.195 × 300 seconds ≈ 3:30:59.
Frequently asked questions
Why is my pace per mile not exactly my pace per km times 1.6?
Because the calculator uses the exact factor 1.609344, not the rounded 1.6 many people use mentally. Over long distances that small difference adds up to noticeable seconds per mile.
What distance does 'half marathon' use?
21.0975 km (13.1094 miles), the standard half marathon race distance. 'Marathon' uses the standard 42.195 km.
Can I use this for cycling or swimming pace?
The time/distance/pace math works for any activity, but the per-km/per-mile display is set up for running paces. For cycling, speed (distance per hour) is usually more useful than pace.
How accurate is the finish-time estimate for a full marathon?
It assumes you hold the exact same pace for the whole distance, which real races rarely do — fatigue, terrain, and pacing strategy all matter. Treat it as a target pace calculator, not a race predictor.
How do I find my 10K finish time if I already know my per-kilometer pace?
Multiply your pace (time per km) by 10, the standard 10K distance already built into this calculator. For example, a 5:00 per km pace over 10 km gives a finish time of 5:00 × 10 = 50:00, using the same 'Time = pace × distance' formula this calculator applies to every distance.