Running Pace Calculator
Pace, time, and distance for any run.
Seconds, m:ss, or h:mm:ss.
Pace per km
- Pace per km
- 5:00 / km
- Pace per mile
- 8:03 / mi
- Finish time
- 25:00
- Distance
- 5 km
Enter time as seconds, m:ss, or h:mm:ss. Pace is shown per km and per mile.
How the pace calculator works
The calculator uses one simple relationship between three quantities: time, distance, and pace. Pace is just time divided by distance. Enter any two of the three and the tool derives the missing one:
- Pace from time and distance:
pace = time / distance - Time from pace and distance:
time = pace × distance - Distance from time and pace:
distance = time / pace
Everything is computed in seconds at full precision, then formatted to mm:ss (or h:mm:ss past an hour) only when the result is shown. Pace is reported in both minutes per kilometre and minutes per mile at the same time. To convert between the two, the tool uses the exact factor 1 mile = 1.609344 km, so seconds per mile equals seconds per kilometre times 1.609344. Distance and pace must both be greater than zero, because each is used as a divisor.
Worked example
Suppose you run 10 km in 50 minutes and want your pace.
| Step | Calculation | Result |
|---|---|---|
| Convert time to seconds | 50 × 60 | 3000 s |
| Pace per km | 3000 / 10 | 300 s/km |
| Format per km | 300 s = 5 min 0 s | 5:00 /km |
| Pace per mile | 300 × 1.609344 | 482.80 s/mi |
| Format per mile | 482.80 s ≈ 8 min 3 s | 8:03 /mi |
So a 50-minute 10K is a 5:00 per kilometre pace, which is about 8:03 per mile. If instead you knew you could hold 5:00 per km and wanted your time over 10 km, the tool would multiply 300 × 10 to give 3000 seconds, or 50:00.
How to use it
- Fill in any two fields (time, distance, pace) and leave the third blank. The calculator solves for the empty one.
- Pick your unit (km or mile) for the distance and pace fields. Results still show both per-km and per-mile pace.
- Enter time as you read it on a watch, for example 50:00 for fifty minutes or 1:45:30 for one hour, forty-five minutes, thirty seconds.
- For race targets, enter the official race distance (5K = 5 km, half marathon = 21.0975 km, marathon = 42.195 km) and your goal time to get the pace you must average.
- For training splits, enter a known pace and a workout distance to see how long the session will take.
Limitations
This tool reports a single average pace and assumes you cover every segment at the same speed. It does not model hills, altitude, wind, heat, road versus track surface, or the slowdown most runners feel in the final miles of a long race. Treadmill belt calibration and GPS drift can also make your watch disagree with the math by a few seconds per kilometre. Use the result as a pacing target and a planning aid, not a prediction of your exact finish, and adjust for course profile and conditions on the day. It is an estimate, not coaching or medical advice.
Frequently asked questions
How do I convert pace per mile to pace per kilometre?
Divide your seconds-per-mile pace by 1.609344 to get seconds per kilometre. For example, 8:00 per mile is 480 seconds, and 480 / 1.609344 is about 298.3 seconds, or roughly 4:58 per km. The calculator does this conversion automatically and shows both at once.
What pace do I need to break a 4-hour marathon?
A marathon is 42.195 km, so a 4-hour finish (14,400 seconds) needs a pace of 14,400 / 42.195, which is about 341.3 seconds per km, or 5:41 per km (about 9:09 per mile). Enter the distance and target time to see the exact pace.
Why is my pace shown as 5:00 instead of 300?
Pace is displayed in minutes and seconds per unit because that is how runners read splits on a watch. 300 seconds per kilometre is the same as 5 minutes per kilometre, written 5:00. The calculator keeps full-precision seconds internally and only formats to mm:ss when it shows the result.
Does this account for hills, wind, or fatigue?
No. It computes a single average pace from the time and distance you enter. Real runs vary with terrain, weather, and how you fade late in a race, so use the average as a planning target rather than a guarantee of even splits.