Running pace and speed explained
Why pace feels backwards
Running pace tells you how long it takes to cover a distance. A smaller number means a faster pace: 4:30 per kilometre is faster than 5:00 per kilometre. Speed measures distance per hour, so a larger number means faster running.
Change the pace in the experiment. At 5:00 per kilometre, speed is 12 km/h and ten kilometres take 50 minutes if the pace stays constant.
Constant pace over the selected distance. This is arithmetic, not a race-time prediction.
Why pace feels backwards
Running pace tells you how long it takes to cover a distance. A smaller number means a faster pace: 4:30 per kilometre is faster than 5:00 per kilometre. Speed measures distance per hour, so a larger number means faster running.
Change the pace in the experiment. At 5:00 per kilometre, speed is 12 km/h and ten kilometres take 50 minutes if the pace stays constant.
Convert pace to speed
First convert minutes and seconds per kilometre into seconds. Then divide 3,600 by that number to get kilometres per hour. For 5:00 per kilometre, 3,600 ÷ 300 is 12 km/h.
The relationship is not linear: taking 30 seconds off a fast kilometre changes speed by more than taking 30 seconds off a slower one. The calculator keeps the units visible so you can check the result.
Estimate a steady finish time
Multiply seconds per kilometre by kilometres, then convert the result to hours, minutes and seconds. At 5:00 per kilometre, 21.1 kilometres would take 1:45:30 at exactly that pace.
The result describes constant pace, not the finish time your fitness guarantees. Hills, wind, stops, fatigue and the exact course distance can all change the outcome.
Use pace in context
GPS pace can jump around, particularly near buildings or trees. A kilometre split smooths those fluctuations but can hide surges within the kilometre.
Compare similar routes and conditions, and look at heart rate and how the effort felt alongside pace. Uphill and downhill running make a single pace target less informative.
How a small pace change accumulates
At 5:00 per kilometre, ten kilometres take 50 minutes at constant pace. At 4:45 per kilometre, the same distance takes 47 minutes 30 seconds: fifteen seconds per kilometre accumulates to two and a half minutes over ten kilometres.
That arithmetic does not mean cutting fifteen seconds per kilometre costs the same amount of effort for everyone. The distance, terrain and your ability to sustain the new pace determine whether it is realistic. Use the calculator to understand the consequence of a pace, not to promise a race result.
Why pace and effort can disagree
Running uphill at the same pace generally requires a different effort from running on the flat. Wind, surface, turns and heat also affect how a pace feels. A steady effort over rolling terrain may produce variable pace even when the runner is pacing well.
Heart rate and perceived effort add context, but heart rate can lag a sudden change in workload and drift during a long session. Use them alongside the route and the pace trace rather than expecting one signal to explain everything.
Miles, kilometres and watch settings
Pace must always include its distance unit. Five minutes per kilometre and five minutes per mile are very different speeds. Switching a watch from kilometres to miles changes the displayed number, not how fast the athlete ran.
GPS distance, auto-pause and whether splits are based on elapsed or moving time can also change an apparent average. Check the settings before comparing two devices or a watch with an officially measured course.