Pace Calculator
Give the calculator any two of distance, time and pace and it works out the third, then shows what that pace means over 5K, 10K, the half marathon and the marathon. Kilometers or miles, your choice.
Splits assume an even pace on the standard course lengths: 5 km, 10 km, 21.0975 km for a half marathon and 42.195 km for a marathon. Real races are never perfectly even — hills, heat and crowds cost time, and most runners slow over longer distances, so treat the marathon split as a best case rather than a prediction.
Formula and calculation
Worked example
A 10K in 50:00 is a pace of 5:00 per kilometer, which is 12 km/h. Holding that pace would bring you home in 1 h 45 min 29 s in a half marathon and 3 h 30 min 59 s in a marathon — on paper, at least, because an even pace over 26.2 miles is the hard part.
When the splits are too optimistic
The splits here assume the same pace for every distance, and runners rarely manage that. Longer races are run slower per kilometer — the classic rule of thumb, Riegel's formula, says finish time grows a little faster than distance: time for the longer race is about the shorter time multiplied by the distance ratio raised to the power 1.06. The gap is small over 5K to 10K and grows by the marathon. So use the splits to convert a pace you already have, or to check what a goal time demands — a sub-2-hour half is 5:41 per kilometer, a 4-hour marathon is 5:41 per kilometer too — and use a recent race result if you want a serious prediction.
What the results mean
- Pace (min per km)
- Your pace in minutes and seconds per kilometer or mile, written the way runners write it — 5:30 means five and a half minutes for each one. It is time divided by distance.
- Speed (km/h)
- Average speed in kilometers per hour, or miles per hour if you picked miles. Speed is the inverse of pace: 5:00 per kilometer is exactly 12 km/h.
- Time
- The finish or elapsed time, shown as hours, minutes and seconds. When you entered the time yourself, this simply echoes it back with the seconds spelled out.
- Distance (km)
- The distance covered in the unit you chose. When you entered the distance yourself, this echoes it back alongside the pace it produced.
- 5K split
- How long 5 km takes at this pace — the standard parkrun and road-race distance. It is the quickest way to see what today's pace means at the weekend.
- 10K split
- How long 10 km takes at this pace — double the 5 km split, and the distance most runners use for a tempo check.
- Half marathon split
- How long the half marathon takes at this pace: 21.0975 km, or 13.109 miles. The official course length is what makes this figure exact rather than rounded.
- Marathon split
- How long the full marathon takes at this pace: 42.195 km, or 26.219 miles. Treat it as a best case — almost nobody holds a short-race pace for a marathon.
Frequently asked questions
What counts as a good running pace?
It depends entirely on the distance and the runner. Brisk walking is around 12 to 15 minutes per kilometer, an easy jog 7 to 8, a regular club runner races somewhere near 5 to 6, and the fastest amateurs go below 4. The useful comparison is against your own recent races, not against a number in a table.
How do I convert pace to speed?
Divide 60 by the pace in minutes per kilometer. A 5:00 per kilometer pace is 60 / 5 = 12 km/h. In miles it works the same way: 8:00 per mile is 60 / 8 = 7.5 mph. The calculator shows both directions automatically, so you can enter whichever one you know.
What is a split, and how is it different from pace?
Pace is a rate — time per kilometer or mile. A split is a time at a point: your 5K split is how long the first 5 km took. Race apps show both, and a negative split (running the second half faster) is usually a sign the race was paced well. The splits here are what your current pace would give you over each classic distance.
Why does the marathon split look faster than my real marathon time?
Because it assumes the pace holds for 42.195 km, and it almost never does. Heat, hills, crowd traffic and the simple fact of running for hours all add time, and most runners slow by several percent in the later stages. A realistic marathon goal is usually 5 to 10 percent slower than the even-pace split, especially if the pace you entered came from a 10K.
Can I use this for treadmill or cycling conversions?
Yes for the arithmetic: the pace, speed, time and distance triangle is the same everywhere. Treadmill speeds are set in km/h or mph, so enter your time and distance from the display and the calculator turns them into a pace you can compare with outdoor runs. One caveat: treadmills are usually a little easier than the road, so treat the outdoor equivalent as slightly slower.