Running Pace Calculator
Find running pace, finish time or distance, convert min/km to min/mile, and get even splits and Riegel race predictions from 1500 m to the marathon.
The interactive tool loads here when JavaScript runs.
About this toolWhat is the Running Pace Calculator?
The Running Pace Calculator solves the three-way relationship between distance, time and pace. Choose which one you want, fill in the other two, and the result appears instantly in both minutes per kilometre and minutes per mile, along with speed in km/h and mph and the time for one 400 m lap. Buttons fill in the 5K, 10K, half marathon, marathon and mile distances.
Below the result you get an even-pace split table, by kilometre or by mile, for printing on a wristband or loading into a watch. If your input is a real race or time trial, the prediction table uses Peter Riegel's formula to estimate equivalent times from 1500 m up to the marathon.
Times can be typed as h:mm:ss, mm:ss or plain minutes. Everything runs in your browser.
- Solve for pace, time or distance
- min/km and min/mile at once, plus km/h, mph and 400 m lap time
- Presets for mile, 5K, 10K, half marathon and marathon
- Even-pace split table by km or mile
- Riegel race predictions from 1500 m to the marathon
How to use the Running Pace Calculator
- Pick Pace, Finish time or Distance under Calculate.
- Enter the two known values. Use the preset buttons for common race distances, and the unit menus to switch between km, miles and metres or between per km and per mile.
- Read pace per km and per mile, finish time, distance, speed and lap time.
- Switch the split table between kilometres and miles to see cumulative times at every marker.
- Check the Riegel predictions if your input was a real race effort, then copy a summary or link.
Worked examples
10K in 50 minutes
Input
Distance 10 km, time 50:00
Output
5:00 per km, 8:03 per mile, 12.0 km/h
The Riegel table predicts 23:59 for 5K, 1:50:19 for the half marathon and 3:50:01 for the marathon from this one result.
Marathon goal of 4 hours
Input
Distance 42.195 km, time 4:00:00
Output
5:41 per km, 9:09 per mile
The split table shows 28:26 at 5 km and 56:53 at 10 km, putting halfway at exactly 2:00:00. Reaching halfway in 1:58 already means running about 6 seconds per km too fast.
How far in an hour at 9:00 per mile
Input
Solve distance, time 1:00:00, pace 9:00 /mile
Output
10.73 km (6.67 miles)
Switching to finish time with the half marathon preset at the same pace gives 1:57:59.
Background and insight
Pace is time divided by distance, so the arithmetic is simple; the traps are units. A mile is exactly 1,609.344 m, so a pace per mile is 1.609344 times the pace per kilometre: 5:00 per km is 8:02.8 per mile, which displays as 8:03. The official half marathon is 21.0975 km and the marathon 42.195 km, the distance fixed for the 1908 London Olympics and adopted as standard in 1921.
Peter Riegel, a research engineer and marathoner, published his endurance model in Runner's World in 1977 and in American Scientist in 1981: T2 = T1 × (D2 / D1)^1.06. The exponent above 1 captures the fact that pace slows as distance rises. It fits well between about 3.5 minutes and 4 hours of running for trained athletes. For less experienced runners the marathon prediction is usually optimistic, because fuelling, heat and training volume start to matter more than raw speed.
Even splits are the default because evidence from world record runs shows that near-even or slightly negative pacing is most economical for distances over 1500 m. Most recreational runners start too fast; a split table is a simple guard against that.
Common use cases
Race-day pacing plan
Turn a goal time into km or mile splits to check on your watch during the race.
Choosing a realistic goal
Use a recent 5K or 10K to predict a half marathon or marathon before committing to a target.
Treadmill speed
Convert a road pace into km/h or mph to set the treadmill.
Track sessions
Read the 400 m lap time for a target 5K or mile pace.
Tips and limitations
- Predictions assume equal training for both distances. Without long runs of 25 km or more, add 5 to 10% to the marathon prediction.
- Use a race result, not a training run, as the input. Easy runs predict nothing useful about race times.
- Hills, heat above about 15 °C and wind all slow pace. Adjust the goal, not the effort.
- GPS watches often measure courses slightly long. Running the tangents matters; check your pace against the official km markers.
- A small negative split, the second half 1 to 2% faster than the first, is a safer plan than banking time early.
Frequently asked questions
How do I convert pace per km to pace per mile?
Multiply the seconds per km by 1.609344. 5:00 per km is 300 s × 1.609344 = 482.8 s, or 8:03 per mile. To go the other way, divide by 1.609344.
What pace do I need for a sub-4-hour marathon?
An even 5:41 per km gives 3:59:48, and 9:09 per mile is about the same. Most runners aim a few seconds per km faster to allow for crowded starts, water stations and GPS drift.
How accurate is the Riegel race predictor?
For distances between the mile and the half marathon it is often within 2 to 3% for trained runners. Marathon predictions from short races tend to be too fast for people who run less than about 50 km a week, sometimes by 10% or more.
What is a good 5K pace for a beginner?
Many new runners finish their first 5K between 30 and 40 minutes, a pace of 6:00 to 8:00 per km. The right pace is one where you could still speak in short sentences for most of the run.
How long is a half marathon in miles?
13.1094 miles, or 21.0975 km. Half of the 26.2188 mile marathon.
Can I enter time as plain minutes?
Yes. A single number is read as minutes, so 50 means 50:00. Use colons for hours and seconds, as in 1:45:30 or 25:15.
Is there an in-depth guide to the Running Pace Calculator?
Yes. “Training Numbers Explained: Pace, Heart Rate Zones, 1RM and METs” covers the background, how it works, common pitfalls and worked examples. Read the full guide.
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