How this calculator works
Running pace is the time taken to cover one kilometre, and speed is the distance covered in one second. They are reciprocals, so a faster pace always means a higher speed. This page converts the chosen race distance to metres, then divides the run time by the distance to get seconds per kilometre. The split table applies that pace evenly, so every full kilometre carries the same time and the final row covers any partial kilometre. The chart plots elapsed time against distance and is a straight line when the pace is constant.
Formula
Pace (seconds per km) = time in seconds / distance in km. Time = pace x distance in km. Distance = time / pace x 1000. Pace per mile = pace per kilometre x 1.609344. Speed (m/s) = distance in metres / time in seconds.
Worked example
A 10 km run in 50:00 is 3,000 seconds over 10 km, so the pace is 300 seconds per kilometre, or 5:00. Pace per mile is 300 x 1.609344 = 482.8 seconds, or 8:03. At that pace each kilometre split falls exactly 5 minutes apart, and the 5 km mark is 1,500 seconds, or 25:00. Holding 5:00 per kilometre for a half marathon predicts 300 x 21.0975 = 6,329 seconds, or 1:45:29.
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Frequently asked questions
What is the difference between pace and speed?
Pace is how long one unit of distance takes; speed is how much distance one unit of time covers. They carry the same information. Runners usually think in pace because it maps directly to split times.
Why does my split pace drift when I only change one input?
Distance, time and pace are linked. Changing one while holding another fixed necessarily changes the third. The mode selector shows which two values you are treating as known.
Should I enter moving time or total time?
Moving time excludes stops and gives the pace held while running. Total time includes traffic lights, aid stations and pauses, so it gives a slower average. Use the same basis for every run you compare.
How do I convert a treadmill speed to pace?
Treadmill speed is usually shown in km/h. Divide 3,600 by the speed in km/h to get seconds per kilometre. A treadmill at 12 km/h is 3,600 / 12 = 300 seconds per kilometre, or 5:00.