Running Pace Calculator

How to use the running pace calculator

1. In Calculate, choose what you want to find: Pace (from distance and time), Finish time (from distance and pace) or Distance (from time and pace). The field you are solving for is hidden.
2. Pick a Race distance (5K, 10K, half marathon, marathon) or type any Distance, in km or mi.
3. Type the Time (h:mm:ss), for example 55:00 or 1:45:30. A plain number is read as minutes.
4. Type the Pace (m:ss) and choose its unit, min/km or min/mi. Switching the unit converts the value already typed.
5. Read your pace per km and per mile, your speed in km/h and mph, the finish time and the distance, with the calculation steps.
6. Below, check the Race time predictions (Riegel, estimate) and the Splits table. Under Split every, choose 1 km or 1 mile.

All calculations happen in your browser. Clear empties the fields.

Pace, time and speed

Pace and speed are two views of the same thing. Pace is time per distance, the number most runners use; speed is distance per time.

• pace = time ÷ distance; 55:00 for 10 km gives 5:30 per km;
• time = pace × distance; a marathon (42.195 km) at 5:30 per km takes 3:52:04;
• speed (km/h) = 60 ÷ pace in minutes; 5:30 per km (5.5 min) is 10.91 km/h.

One mile is exactly 1.609344 km, so 5:30 per km is 8:51 per mile. The half marathon is 21.0975 km and the marathon 42.195 km (World Athletics).

Race predictions with Riegel’s formula

In 1981, engineer Peter Riegel noticed that world records over very different distances line up on a simple power law (American Scientist, 1981):

T2 = T1 × (D2 ÷ D1)^1.06

The exponent 1.06 means you slow down a little as the distance grows. Example: a 5K in 25:00 predicts about 52:07 for 10K, 1:55:00 for the half marathon and 3:59:47 for the marathon.

Treat these times as estimates, not targets. The formula assumes you are equally well trained for both distances. Many recreational runners fall short of the marathon prediction because long runs, fuelling and pacing matter more over 42 km. Riegel fitted the formula to efforts of roughly 3.5 minutes to 4 hours, so the tool warns you when your result is outside that range. Predictions from a recent race, run all-out on a flat course, work best.

Using the split table

Each row shows the distance reached and the elapsed time at an even pace, including a final partial split (for example 3.11 miles in a 5K). Print it or copy it onto a wristband. Pacing evenly, or finishing slightly faster than you start, is usually the most efficient way to race.

Limits

Heat, hills, wind, altitude and fatigue slow you down, and GPS watches often measure a slightly different distance. If you are new to running, have a heart condition or have not trained for a while, ask a doctor before starting hard sessions or racing.