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Running Pace Calculator

One run in, every race prediction out.

Pace math trips everyone up mid-run: what is 4:55 per km in miles, and what does today's 10K say about your marathon? This calculator converts any distance and time into pace per kilometer and per mile, overall speed, and equivalent race times at the four classic distances using the Riegel formula — the standard race-equivalency model used by coaches.

Why people use this

Runners use this mid-training-block to convert treadmill speed to pace, to see what a 10K time predicts for a marathon, and to set honest race-day targets. Coaches use it to write workouts — "4:55/km" means nothing until you see it per mile or as a finish time.

How it works

1. Enter the distance you ran (km or miles) and your time in hours, minutes, seconds.
2. Read your pace per km, pace per mile, and speed instantly.
3. The Riegel formula (T₂ = T₁ × (D₂/D₁)^1.06) predicts equivalent times for 5K through marathon.
4. Predictions assume equivalent training for the distance — a 5K time does not guarantee a marathon without the mileage.

Common questions

How accurate is the Riegel prediction?

Within a few percent for runners trained for both distances. It overestimates marathon performance for runners whose training is short and fast — endurance is a separate adaptation from speed.

What is a good running pace?

Context is everything: average 5K finish times cluster around 6:30–7:30 per km for recreational runners, sub-4:00 per km is competitive amateur, and elites run under 3:00. Compare against your own history first.

How do I convert treadmill speed to pace?

Treadmills display speed (km/h or mph): pace is 60 ÷ speed. 12 km/h is exactly 5:00 per km. The calculator converts automatically — enter a 1 km run at the time it takes at that speed.

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