Running pace per kilometre:
convert it to speed, miles and race times

Pace is time per distance, speed is the reverse

Pace tells you how long each kilometre takes. Speed tells you how many kilometres you cover in an hour. A runner holding 5:30 per km is moving at 10.9 km/h, and both numbers describe the same effort. Most road races and watches use pace because it is easy to check at every kilometre marker.

The two are reciprocals, which means a smaller pace figure is a faster runner. A 5:00 pace beats 6:00, even though 6 looks bigger. Keeping that in mind avoids a lot of confusion when you read training plans that mix km/h from treadmills with min/km from watches.

Treadmills usually show speed, while outdoor apps show pace. A pace calculator removes the arithmetic when you move between them.

The pace, speed and finish-time formulas

Worked example: a 10K in 55 minutes

A runner wants to finish a 10 km race in 55:00 and asks what pace and speed that requires.

If the same runner can hold 5:30 per km over a half marathon, the time is 21.0975 × 5.5 = 116.04 minutes, or 1:56:02. A marathon at that pace would take 42.195 × 5.5 = 232.07 minutes, or 3:52:04, though few people hold the same pace for four hours as they do for one.

Pace chart for common race distances

Use the table to find your row, then read across. Half and full marathon times are rounded to the nearest second.

Every extra 30 seconds per kilometre adds 2:30 to a 5K, 5:00 to a 10K, about 10:33 to a half marathon and about 21:06 to a marathon. That scale is why small pace changes matter more the longer the race is.

Pace per mile and treadmill speeds

To change min/km into min/mile, multiply by 1.609344. To go the other way, divide. A 9:00 per mile pace is 9 ÷ 1.609344 = 5.59 min/km, or about 5:36 per km. The speed in km/h is 60 divided by that, about 10.7 km/h.

Treadmills in many countries show km/h, others show mph. For quick reference: 8 km/h is a 7:30 pace, 10 km/h is 6:00, 12 km/h is 5:00 and 14 km/h is about 4:17. Keep one chart pinned near the treadmill if you switch between outdoor and indoor sessions.

• Pace per km to km/h: 60 ÷ pace in decimal minutes.
• Pace per km to pace per mile: multiply by 1.609344.
• km/h to mph: multiply by 0.621371.
• Marathon distance: 42.195 km, or 26.2 miles.

Predicting a longer race from a shorter one

An even-pace chart shows what is possible if you never slow down. A simple prediction rule, often called the Riegel formula, accounts for the slowdown that comes with distance. It scales your known time by the ratio of the two distances raised to the power 1.06.

Starting from a 10K in 55:00, the half marathon prediction is 55 × (21.0975 ÷ 10)^1.06 ≈ 121.4 minutes, or about 2:01:21. That is slower than the 1:56:02 an even 5:30 pace would give, and it is the more realistic figure. The marathon prediction from the same 10K is about 4:13:01.

The rule works best between similar distances and for runners with the endurance training to match. It overestimates a marathon for people who run low mileage. Use it to set a first target, then refine it with long training runs at the pace you plan to race.

Training paces are usually set relative to race pace. Easy runs are often an appreciable amount slower than 10K pace, commonly by a minute or more per kilometre, so that the body can recover between harder days. If your 10K pace is 5:30, an easy run near 6:30 to 7:00 per km is typical, which is 8.6 to 9.2 km/h. Tempo efforts sit a little slower than race pace and intervals a little faster. These bands are rough guides, and a heart-rate monitor or the talk test is a good cross-check.

Why a predicted time can be too optimistic

The table assumes the same pace from start to finish. Real races rarely go that way. Starting a 10K at 5:15 and fading to 5:50 gives a slower overall time than holding 5:30, because the early speed borrows energy you pay back later. Even or slightly negative splits are the safest plan.

• Course profile: hills, turns and crowds in the first kilometres add seconds that a flat chart ignores.
• Weather: heat and humidity can slow the same effort by several percent.
• Distance error: a watch can read 10.1 km over a measured 10 km course because of GPS drift and weaving, so check against marker boards.
• Fatigue: pace for a marathon is usually well below your 10K pace, not the same number.
• Training: predictions from a recent race are more reliable than from a hopeful guess.

Use the chart as a planning tool, rather than a promise, and build up distance gradually. People with medical concerns should talk to a clinician before taking on a long-distance goal.