How to Calculate Running Pace and Finish Time

Runners usually think in pace, minutes per kilometer or mile, rather than speed. The math is the speed formula turned upside down.

Pace from time and distance

A 10 km run in 55 minutes: 55 ÷ 10 = 5.5 minutes per km, which is written 5:30 per km (half a minute is 30 seconds).

Finish time from pace

At 5:30 per km, a half marathon (21.0975 km) takes 5.5 × 21.0975 ≈ 116 minutes, or about 1:56:02.

Pace and speed

5:30 per km is 60 ÷ 5.5 ≈ 10.9 km/h. To switch to miles, multiply a per-km pace by 1.609: 5:30 per km is about 8:51 per mile.

Common race distances

• 5K: 5 km (3.11 miles)
• 10K: 10 km (6.21 miles)
• Half marathon: 21.0975 km (13.1 miles)
• Marathon: 42.195 km (26.2 miles)

Predicting a longer race

Pace slows as distance grows, so doubling your 10K time underestimates your half marathon. A widely used estimate is Riegel's formula:

From a 55-minute 10K, the predicted half marathon is 55 × (2.10975)^1.06 ≈ 121 minutes, roughly 2:01. Treat it as a guide; it assumes you've trained for the longer distance.

Even splits

Many coaches suggest starting at, or slightly slower than, your goal pace. Going out too fast usually costs more time later than it saves early on.