Running Pace Calculator
Enter any two of distance, time and pace to get the third, convert pace and speed between kilometers and miles, estimate a race time at another distance and see the splits
Your Run
Type plain numbers; a decimal point or comma both work. Minutes and seconds go in separate boxes, so 5:30 is 5 and 30, not 5.30. Your inputs stay in your browser.
Pace = time ÷ distance = 50:00 ÷ 6.2137 mi = 8:03 per mile
At 8:03 per mile: 5K 25:00, 10K 50:00, half marathon 1:45:29, marathon 3:30:59.
| Mark | Split time | Total time |
|---|---|---|
| mile 1 | 8:03 | 8:03 |
| mile 2 | 8:03 | 16:06 |
| mile 3 | 8:03 | 24:08 |
| mile 4 | 8:03 | 32:11 |
| mile 5 | 8:03 | 40:14 |
| mile 6 | 8:03 | 48:17 |
| Finish (6.2137 mi) | 1:43 | 50:00 |
Rows every 1 mi; the split time covers the stretch since the previous row.
How to use it
- Pick what you want to find: the pace, the finish time, the distance, a race time at another distance, or a pace-speed conversion.
- Choose metric or US units. Pick a standard distance, or choose Custom distance and type your own.
- Type the time as hours, minutes and seconds in separate boxes, and the pace as minutes and seconds per kilometer or mile.
- For a race-time prediction, enter the race you know (distance and time) and the distance to predict. The fatigue factor is set to the common 1.06 and you can change it.
- Read the result, the steps, the finish times at that pace and the splits. Use the split option for an even pace or a negative split, and Copy Result for a message.
Worked example
A 10 km run in 50:00 is a pace of 50:00 ÷ 10 = 5:00 per km, which is 8:03 per mile, or 12 km/h (7.46 mph). Kept up for a marathon (42.195 km) that pace gives 3:30:59, and for a half marathon 1:45:29. For a prediction instead, 10 km in 50:00 with the 1.06 factor gives 1:50:19 for the half marathon, an average of 5:14 per km. Reverse it: at 5:30 per km, 10 km takes 55:00, because 5:30 is 5.5 minutes, not 5.30.
Why this tool exists and where its numbers come from
Pace is simple arithmetic, but runners mix up minutes and decimals, kilometers and miles, and a prediction at another distance is a model, not a measurement. The sources below cover the mile conversion, the marathon distance and the prediction formula with its limits. They do not cover training zones, heart rate or health advice, which this tool does not calculate.
Sources
- NIST SP 811, Appendix B: conversion factors
- AIMS: world records page, quoting World Athletics rules
- P. S. Riegel, Athletic Records and Human Endurance, American Scientist 69(3), 1981 (PDF copy hosted by Northern Kentucky University)
- Wikipedia: Peter Riegel
For the full method, see the Methodology section just below.
Methodology
The arithmetic. Pace is time per distance: p = t ÷ d. Time is t = p × d and distance is d = t ÷ p. Speed is distance per hour, so with the pace in minutes per unit, v = 60 ÷ p. Miles and kilometers are linked by 1 mile = 1.609344 km, so a pace per mile is the pace per kilometer × 1.609344. The prediction. The race-time estimate uses T2 = T1 × (D2 ÷ D1)f, with f = 1.06 unless you change it. Negative splits. With a difference g between the halves, the first half runs at the average pace + g ÷ 2 and the second at the average − g ÷ 2, so the total time does not change. Results are shown to the nearest second.
Sources and documentation
The mile conversion comes from the first entry, the marathon distance from the second, and the prediction formula, its range and its caveats from the third; the fourth gives the origin of the formula and the criticism for long distances. The half marathon is taken as exactly half of the marathon. Pages were consulted in October 2026.
- NIST SP 811, Appendix B: conversion factorsInternational mile = 1,609.344 m, marked as exact.
- AIMS: world records page, quoting World Athletics rulesQuotes World Athletics Rule 260.28 listing the Marathon as 42.195 km.
- P. S. Riegel, Athletic Records and Human Endurance, American Scientist 69(3), 1981 (PDF copy hosted by Northern Kentucky University)Power law t = a·x^b, fatigue factor about 1.08 for world-class running and 1.05 to 1.06 for men aged 40 to 70, endurance range of about 3.5 to 230 minutes, and “not a fundamental theory”.
- Wikipedia: Peter RiegelFormula first proposed in Runner’s World in August 1977, widely adopted, and modified by some sites because it gives seemingly unachievable predictions for longer distances.
Where pace sums go wrong
- Reading 5:30 as 5.30. A pace of 5:30 per km is 5.5 minutes, so 10 km takes 55:00. Reading it as 5.30 minutes (5:18) gives 53:00, two minutes too fast.
- Mixing kilometers and miles. A pace of 8:00 per mile is 4:58 per km, not 8:00 and not 5:00.
- Calling the marathon 26 miles. It is 26.22 miles (42.195 km). At 9:00 per mile the missing 0.22 miles are 1:58: 3:54:00 for 26 miles against 3:55:58 for the real distance.
- Calling the half marathon 21 km. It is 21.0975 km. At 5:00 per km, 21 km takes 1:45:00 and the half marathon 1:45:29.
- Trusting a long-distance prediction. 5 km in 25:00 gives 3:59:47 for the marathon with the 1.06 factor, an average of 5:41 per km. Treat predictions at much longer distances as a ceiling for a good day, not a plan.
Estimate for information only, not training or medical advice.
Gear for the Run
A GPS watch to check the real pace, a belt to carry the phone and a roller for the legs afterwards
Garmin Forerunner 55, GPS Running Watch with Daily Suggested Workouts, Up to 2 Weeks of Battery Life, Black - 010-02562-00
A GPS running watch with daily suggested workouts and up to 2 weeks of battery life, according to the listing; handy for checking the real pace against the plan.
Fitgriff® Running Belt for Men & Women - Secure Jogging Pouch for Phone, Keys & Essentials - For All Cell Phones
A jogging pouch for phone, keys and essentials that is listed as fitting all cell phones, according to the listing.
Amazon Basics High-Density Foam Roller for Exercise and Recovery, 18 Inches, Black
A high-density 18-inch foam roller in black for exercise and recovery, according to the listing.
As an Amazon Associate we earn from qualifying purchases at no additional cost to you.
Frequently asked questions
How do I calculate running pace? ▼
Divide your time by your distance. A 10 km run in 50:00 is 3,000 seconds ÷ 10 km = 300 seconds per km, which is a pace of 5:00 per km (8:03 per mile). Choose “Pace” in the tool, type the distance and the time, and it does the sum for you.
How do I convert min/km to min/mile and to km/h? ▼
Multiply a pace per km by 1.609344 to get the pace per mile, and divide by 1.609344 to go back. For speed, divide 60 by the pace in minutes: 5:00 per km is 5 minutes, so 60 ÷ 5 = 12 km/h. Remember 5:30 is 5.5 minutes, not 5.30.
How accurate is the race-time prediction? ▼
It is an estimate. It uses a rule of thumb from Riegel with a fatigue factor of 1.06, and Riegel’s paper reports different factors for different groups and limits the relationship to efforts of about 3.5 to 230 minutes. Predictions at much longer distances tend to be optimistic. Change the fatigue factor to see how sensitive the answer is.
What is a negative split? ▼
Running the second half of a race faster than the first. In the tool, choose “Negative split” and set how many seconds per km or mile faster the second half is; the first half is slower by the same total, so the finish time stays the same.
What distances does the tool use for a marathon, a half marathon and a mile? ▼
The marathon is 42.195 km (26.22 miles), the half marathon is half of that, 21.0975 km (13.11 miles), and a mile is exactly 1.609344 km.
Does it account for hills, weather or my watch’s GPS? ▼
No. It uses the distance and time you enter, evenly spread. A GPS watch can read a little differently from the official distance, so the pace on your watch and the pace worked out from the official distance may not match exactly.