Running pace calculator: pace, time, speed and splits

A running pace calculator for any distance

This pace calculator links three things: distance, time and pace (or speed). Enter any two and it works out the third. Use it to set a goal pace for a 5K, to see what a marathon pace means as a finish time, or to turn min per km into mph for the treadmill. Everything runs in your browser.

How to use it

1. On the "Calculator" tab, fill in two of "Distance", "Time (h:min:s)", "Pace" and "Speed". The calculated box turns green. "Quick distances" fill in the distance in one click: 5 km, 10 km, half marathon (21.0975 km), marathon (42.195 km), 1 mile, 100 m and 400 m.
2. Type times the way you think of them: "45:30" means 45 min 30 s, "1:45:00" and "1h45" mean 1 hour 45 minutes, and a plain "50" means 50 minutes.
3. The page starts in "Miles": pace in min/mile, speed in mph. Press "Kilometres" to switch to min/km and km/h at any time.
4. "How it is worked out" shows every formula with your numbers.

Pace or speed: why runners think in minutes per mile

Speed tells you how far you go in an hour; pace tells you how long one mile (or kilometre) takes. They describe the same effort: 7.5 mph is an 8:00 mile. Runners prefer pace because it matches the mile markers and adds up easily: at 8:00 per mile you pass mile 5 at 40:00. Treadmills, on the other hand, are set in mph or km/h.

The formulas, with exact examples

• Pace = time ÷ distance: 10 km in 50:00 is 3,000 s ÷ 10 = 300 s, so 5:00 min/km.
• Speed = 3,600 ÷ pace in seconds: 3,600 ÷ 300 = 12 km/h. With 1 mile = 1.609344 km, 5:00 min/km is 8:02.8 min/mile and 7.46 mph.
• Time = distance × pace: a marathon at 5:00 min/km is 42.195 × 300 = 12,658.5 s, or 3:30:58.5. The tool shows 3:30:59: times are rounded to the nearest second and half a second rounds up, while the working keeps the tenth.
• A marathon at 8:00 per mile is 26.2188 mi × 480 s = 12,585 s, so 3:29:45.

Finish times by pace

Setting a goal and choosing your pace

Start from a recent race or time trial, not from a round number. Enter the distance and the time you are aiming for: the pace you get becomes the number to watch on your watch. Try it over a few miles in training before you commit to it on race day.

Split times and pacing a race

The "Split times" tab takes the distance and pace from the calculator and lists the running time and the segment time at every mile (or kilometre) and at key distances. A 10K at 5:00 min/km gives 5:00, 10:00, 15:00… 50:00. Tick "Negative split" to run the second half faster: at 2%, a 5K in 25:00 becomes 12:38 for the first half and 12:22 for the second, with the same total. A slightly easy start costs little and saves a lot over the last miles.

What the race predictor leaves out

The "Race predictor" tab uses the Riegel formula: T2 = T1 × (D2 ÷ D1)^1.06. From a 5K in 25:00, the 10K estimate is 1,500 s × 2.0849 = 3,127.4 s, or 52:07. From 10 km in 45:00, it gives 1:39:17 for a half marathon. It assumes you have trained for the target distance and ignores hills, heat, wind and specific training; for a marathon without long runs it is often too optimistic.

These are general pointers, not medical advice. See a doctor before starting hard training, build up gradually and slow down if you feel pain or it is very hot.

Frequently asked questions

How do I convert min per km to mph?

Multiply the pace in seconds by 1.609344 to get seconds per mile, then divide 3,600 by it: 5:00 min/km gives 482.8 s, and 3,600 ÷ 482.8 = 7.46 mph. The "Pace ↔ speed" tab does it and shows a chart from 3:00 to 8:00 min/km.

Why is "3:30" read as 3 minutes 30 seconds?

Two numbers separated by a colon are read as minutes and seconds. For three and a half hours, type "3:30:00" or "3h30".

What marathon pace do I need to break 4 hours?

14,400 s ÷ 26.2188 mi = 549.2 s, so 9:09.2 per mile. At an even 9:09 you finish in 3:59:54.

Are my settings sent anywhere?

No. Your last settings stay on this device, and "Clear all" removes them.