Running Pace Calculator
Free running pace calculator — find your pace from a finish time, or predict finish time from a target pace. Works for km and miles. Runs in your browser.
Pick a mode, fill the relevant fields. The calculator gives back pace, total time, or distance — whichever you asked for.
The formulas
pace per unit = time ÷ distance
time = pace × distance
distance = time ÷ pace
That’s it. Same arithmetic, three rearrangements. Express time in seconds under the hood, then convert back to mm:ss for display.
km vs mile
The math doesn’t care which unit you use — but pick one and stay consistent. 5:00/km ≈ 8:03/mile. 8:00/mile ≈ 4:58/km. If your event is a marathon (42.195 km / 26.219 mi), even a small unit mix-up matters.
Limits of constant-pace math
This calculator assumes a flat, constant-pace run. Real races have fatigue, hills, weather and pacing strategy. Empirical race-prediction formulas (e.g. Riegel: T₂ = T₁ × (d₂ / d₁)^1.06) account for the typical slowdown over longer distances. We may add that as a separate race-time prediction page.
Worked examples
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10 km in 50:00 → 5:00/km
Pace: 5:00 per km
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Run 10 km at 5:00/km — total time?
Total time: 50:00
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25:00 at 5:00/km — distance?
Distance: 5 km
Frequently asked questions
How is pace calculated?
pace per unit = total time ÷ distance. We display it as mm:ss per km (or per mile). To go in reverse — predict the time for a target pace — multiply pace × distance.
Should I track pace per km or per mile?
Whichever your watch and race events use. Most international running uses km; most US road races use miles. 5:00/km ≈ 8:03/mile; 8:00/mile ≈ 4:58/km.
Why does the predicted finish time feel optimistic for a marathon?
Constant-pace math doesn't account for fatigue, hydration, heat or hills. Race-prediction models (e.g. Riegel) factor in slowdown over longer distances. This calculator is the pure arithmetic; for race goals, plan for a slight fade beyond half-marathon distance.
Does this work for cycling or swimming?
The math is the same — time ÷ distance is pace, distance ÷ time is speed. We label the units as running-typical (min:sec/km), but you can repurpose freely. Cycling more commonly uses speed (km/h or mph) than pace.
How precise should I be with seconds?
For training, pace within ±5 sec/km is plenty. For race targets, ±2 sec/km matters — a 2-second-per-km difference across a marathon is over a minute on the clock.
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