Running pace calculator (with splits and treadmill speed)

Running pace is your time divided by your distance. Finish 5 km in 30 minutes and your pace is 6:00 per km, which is 9:39 per mile or 10 km/h on a treadmill. The calculator works it the other way round too: give it a pace and a distance for your finish time, or a time and a pace for how far you'll get.

How the calculator works

Everything comes from one relationship: time = distance × pace. Rearranged, that gives the three modes.

• Pace = time ÷ distance
• Finish time = distance × pace
• Distance = time ÷ pace

Speed is pace turned upside down: km/h = 60 ÷ pace in minutes per km. A 6:00 pace is 60 ÷ 6 = 10 km/h; a 5:30 pace is 60 ÷ 5.5 = 10.9 km/h.

For the race presets the calculator uses the official distances. World Athletics sets the marathon at 42.195 km (26 miles 385 yards), and the half marathon at exactly half that, 21.0975 km. Miles are converted with the international mile of exactly 1.609344 km, as listed in the NIST Guide to the SI.

Worked examples

• Pace: a 10 km run in 1:00:00 is 3,600 s ÷ 10 = 360 s, so 6:00 per km.
• Finish time: a half marathon at 5:41 per km is 21.0975 × 341 s ≈ 7,194 s, or 1:59:54, just under 2 hours.
• Distance: 45 minutes at 6:30 per km is 45 ÷ 6.5 = 6.92 km.

Pace chart: common paces and finish times

Plenty of beginners run slower than 7:00 per km and walk parts of the way. That's normal. The first goal is to cover the distance comfortably, not to hit a number.

Using the numbers on a treadmill

Gym treadmills in India almost always show speed in km/h, so the calculator gives you that number directly. Want to practise a 30-minute 5 km? Set 10 km/h.

A treadmill feels a little easier than the road at the same speed because there's no air resistance. In a study of nine trained male runners, Jones and Doust (1996) found that a 1% incline made the oxygen cost of treadmill running match running on a flat road, over runs of about 5 minutes at speeds from roughly 10.5 to 18 km/h. At the two slowest speeds they tested (about 10.5 and 12 km/h), 0% and 1% both matched the road, so for gentle jogging the incline matters less. The study didn't test walking or very slow running, so treat the 1% tip as a guide for running speeds.

Splits: even pace or negative split

The splits table shows each kilometre's time and your running total, so you can check yourself at every marker.

• Even pace runs every km at the same speed. It's the simplest plan and wastes the least energy.
• Negative split starts about 1% slower than your average and finishes about 1% faster, so the second half is roughly 2% quicker than the first and the finish time stays the same. Starting slightly easy helps you avoid going out too fast and fading later.

If you're training by heart rate rather than pace, the heart rate zone calculator gives your zone 2 range. Easy runs should feel conversational, whatever the watch says about pace.

The race time predictor (Riegel's formula)

The predictor uses a formula published by Peter Riegel, first in Runner's World in 1977 and then in Athletic Records and Human Endurance (American Scientist, 1981):

T2 = T1 × (D2 ÷ D1)^1.06

T1 is your time over distance D1, and T2 is the predicted time over distance D2. The 1.06 exponent means each doubling of distance takes about 2.08 times as long, because you slow down a little as the distance grows. Riegel fitted the equation to world-record performances and described it as working for efforts lasting roughly 3.5 to 230 minutes, so the calculator flags predictions outside that window.

Worked example: a 30:00 5 km predicts about 1:02:33 for 10 km (30:00 × 2^1.06), 2:18:00 for a half and 4:47:44 for a marathon.

How to read it:

• It's most useful between similar distances, such as 5 km to 10 km.
• It assumes you've trained properly for the longer race. A marathon prediction from a 5 km time often turns out optimistic for runners who haven't done the long runs, so treat it as a best case.
• Heat and humidity slow most people down, which matters on an Indian summer morning. Compare like with like.

Limits of this calculator

Pace, speed and split numbers are exact arithmetic, but the inputs aren't always exact. Phone and watch GPS can drift, especially between tall buildings or under trees, so a "5 km" run may not be exactly 5 km. Hills also change the effort a pace represents.

Running burns plenty of energy, so if you're adding it to a weight-loss plan, use the calorie calculator for your daily target and the water intake calculator to plan drinks on hot days. The zone 2 cardio guide explains how easy running fits around weights.

If you're new to exercise, over 40 and inactive, or have a heart condition, high blood pressure, diabetes or chest pain, dizziness or unusual breathlessness when you exert yourself, see a doctor before you start running.

Useful links

• World Athletics: Marathon (42.195 km)
• World Athletics: Half marathon (21.0975 km)
• NIST Guide to the SI, Appendix B.8: conversion factors (mile = 1.609344 km)
• Riegel 1981, Athletic Records and Human Endurance (American Scientist)
• Jones and Doust 1996, A 1% treadmill grade most accurately reflects the energetic cost of outdoor running

This calculator is for general information and isn't medical advice.