Running Pace Calculator — pace per km & mile, speed, from distance and time

How it works

Pace and speed are the same fact stated two ways. Pace is time per unit distance — minutes and seconds per kilometre or per mile, the form runners plan and race by. Speed is distance per unit time — kilometres or miles per hour, the form a treadmill or a car shows. Divide one into 3,600 and you get the other: 12 km/h is 3,600 ÷ 12 = 300 seconds per kilometre, which is 5:00.

Everything here is exact arithmetic. The only fixed numbers are the unit definitions — a mile is exactly 1,609.344 metres — and the official race distances: World Athletics sets the marathon at 42.195 km and the half-marathon at exactly half that, 21.0975 km. The equivalent-times table uses those so you can see what a pace means over a real race.

Worked example

A 5 km run in 25 minutes:

• Pace: 25:00 is 1,500 seconds; over 5 km that's 1,500 ÷ 5 = 300 seconds, or 5:00 per kilometre. Per mile it's 300 × 1.609344 = 482.8 seconds, 8:03.
• Speed: 5 km in 1,500 seconds is 5 ÷ (1,500 ÷ 3,600) = 12 km/h, which is 12 ÷ 1.609344 = 7.46 mph.

Holding that 5:00/km pace, the finish times come straight from the distances: 10K in 50:00, the half-marathon in 21.0975 × 300 = 6,329.25 s (1:45:29), and the marathon in 42.195 × 300 = 12,658.5 s (3:30:59).

Frequently asked questions

What's the difference between pace and speed?

None, mathematically — they are reciprocals. Pace is time per distance (minutes per km); speed is distance per time (km per hour). Runners usually think in pace because it maps directly onto a race plan ("I need 5:00 kilometres"), while speed is what machines display. This page shows both so you don't have to convert in your head.

How do I convert pace between kilometres and miles?

Multiply or divide by the length of a mile in kilometres, 1.609344. A pace of 5:00 per kilometre is 5:00 × 1.609344 = 8:03 per mile, because a mile is longer, so each mile takes more time. Speeds convert the same way: 12 km/h ÷ 1.609344 = 7.46 mph.

Why enter the time as hours, minutes and seconds separately?

Because race times are read that way — a marathon is 3:45:12, not 225.2 minutes. Splitting the field into three keeps you from having to convert your own time into a decimal before you start. The calculator adds them up as hours × 3,600 + minutes × 60 + seconds.

What are the official race distances?

World Athletics, the sport's governing body, sets the marathon at 26 miles 385 yards, which is 42.195 km, and the half-marathon at exactly half of that, 21.0975 km. The 5K and 10K are simply 5 and 10 kilometres. This page uses those figures for the equivalent-times table.

Does this predict my time at another distance?

Not exactly. The equivalent-times table shows what each distance would take **at the same pace** — useful for planning, but real races slow down over longer distances because you can't hold a short-race pace for a marathon. Dedicated race-time predictors (like Riegel's formula) model that fade; this page holds pace constant, which is honest arithmetic rather than a prediction.

Why is my mile pace a bigger number than my kilometre pace?

Because a mile is longer than a kilometre, so covering one takes more time. The per-mile pace is always the per-kilometre pace times 1.609344, the number of kilometres in a mile. A smaller kilometre pace and a larger mile pace can describe the exact same speed — 5:00 per km and 8:03 per mile are the same runner, just measured against a longer unit.

How accurate is this?

The arithmetic is exact — pace and speed follow directly from the distance and time you enter, with no estimation. The only judgement is your measurement: GPS distance can be off by a few percent on a winding course or under tree cover, and that error passes straight through to the pace.