Free Running Pace Calculator
Calculate running pace, finish time or distance in km or miles, with 5K to marathon presets, even splits, km/h and mph, and Riegel race predictions.
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How to calculate running pace, finish time or distance
Enter two of distance, time and pace to get the third, with per-km and per-mile pace, splits and race-time predictions.
- Choose whether to calculate pace, finish time or distance.
- Enter a distance in km or miles, or tap a 5K, 10K, half marathon, marathon or 1 mile preset.
- Type the time as h:mm:ss or mm:ss, and the pace as m:ss per km or per mile. A plain number is read as minutes.
- Read pace in both units, speed in km/h and mph, and the finish time or distance.
- Pick a split unit and interval for the split table, download it as CSV, and check the race predictions.
When runners use a pace calculator
Before a race, it turns a goal time into the pace to hold, such as the per-kilometre pace for a sub-2-hour half marathon, and gives a split table you can write on your arm or program into a watch. After a race or a training run, it converts your time into pace and speed and estimates what you might run over other distances.
It also bridges kilometres and miles. Races in some countries mark miles while your watch shows kilometres, treadmills in gyms around the world show km/h or mph, and training plans may be written in either. The calculator shows every result in both systems at once.
Worked example: 10K in 50 minutes
Enter 10 km and 50:00. The pace is 5:00 per km, which is 8:03 per mile, and the speed is 12.00 km/h or 7.46 mph. The kilometre split table shows 5:00 for each split, with elapsed times of 5:00, 10:00 and so on to 50:00. Switching the split unit to miles gives six full miles at 8:03 and a final partial split to 6.214 miles.
The Riegel predictor then scales that result: about 7:13 for a mile, 23:59 for 5K, 1:16:51 for 15K, 1:50:19 for a half marathon and 3:50:01 for a marathon. These are equal-effort estimates for a runner trained for each distance.
Working the other way: a half marathon at 5:30 per km takes 1:56:02. A 4-hour marathon requires an average of 5:41 per km, or 9:09 per mile.
How the numbers are calculated
Pace is time ÷ distance, time is pace × distance and distance is time ÷ pace. Internally everything is kept in seconds and kilometres. One mile is exactly 1.609344 km, a half marathon 21.0975 km and a marathon 42.195 km. Speed is 3,600 ÷ seconds per km for km/h, and 3,600 ÷ seconds per mile for mph.
Splits assume even pacing: each split takes the same time per unit, and the last split is shorter when the distance is not a whole number of split units. Predictions use Pete Riegel's 1981 formula, T2 = T1 × (D2 ÷ D1)^1.06. The exponent is editable from 1.00 to 1.20; a higher exponent adds more slowing over longer distances, which suits runners with less endurance training.
Common mistakes to avoid
Typing a pace like 5.30 when you mean five minutes thirty seconds is easy to do. In the pace field a plain number means minutes, so 5.30 is read as 5 minutes 18 seconds. Use the colon form, 5:30. Another mistake is predicting a marathon from a 5K: the longer the jump, the less reliable any formula becomes, so predict from the closest recent race you have.
GPS watches often measure a race as slightly longer than its certified distance because runners do not follow the shortest line. If your watch says 10.15 km for a 10K, use the official distance for pace comparisons.
Useful tips and limitations
- Use a recent race or hard time trial as the input for predictions. Easy training runs make every prediction too slow.
- Predictions for the marathon assume you have trained for it; with low weekly mileage, add a safety margin.
- For a negative split, plan the first half 5–10 seconds per km slower than the average shown.
- Download the split CSV and print it as a pace band for race day.
Common questions
How do I convert pace per km to pace per mile?
Multiply seconds per km by 1.609344. A 5:00 per km pace is 300 × 1.609344 ≈ 483 seconds, or 8:03 per mile.
What is the Riegel formula?
T2 = T1 × (D2 ÷ D1)^1.06, published by Pete Riegel in 1981. It scales a known race time to another distance, adding a little extra time for fatigue as distance grows.
How long is a half marathon and a marathon?
A marathon is 42.195 km (26.2 miles) and a half marathon is 21.0975 km (13.1 miles).
What pace do I need for a sub-2-hour half marathon?
About 5:41 per km or 9:09 per mile; enter 21.0975 km and 1:59:59 to see the exact pace and splits.
Can the Running Pace Calculator be used for walking or cycling?
Yes. The maths is the same for any activity; the Riegel predictions were developed for running, so treat them with caution for other sports.
Why is my predicted marathon time faster than I can run?
Riegel's formula assumes you are equally well trained for every distance. Without long runs and enough weekly mileage, real marathon times are often several minutes slower; try an exponent of 1.08 or higher.
Everything you enter is calculated in your browser. Nothing is uploaded and no account is needed. Copy or download your results before leaving the page.