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Running
pace calculator
Enter any two of distance, time and pace and we solve for the third — then project the result across the standard race distances.
Pace, speed and why runners use pace
Speed is distance over time; pace is time over distance. They are the same information inverted, and runners use pace because it is the number you can hold in your head while running. "Five minute kilometres" is checkable at every marker; "12 kilometres per hour" is not.
How race prediction works, and where it lies
Riegel's model says your time scales with distance raised to the power 1.06. If pace held perfectly, the exponent would be 1 — doubling the distance would double the time. The extra 0.06 is the empirical observation that everyone slows as distance grows.
The model works well between neighbouring distances. A 10K predicted from a 5K is usually within a couple of percent, because the physiology is similar and the training that produced one supports the other.
It becomes optimistic across big jumps. A marathon predicted from a 5K assumes you have built the endurance base, practised fuelling, and can hold form for three or four hours. The formula cannot see any of that. Treat a marathon prediction from a parkrun as a ceiling on a good day rather than a plan.
Do not train at your predicted pace
The most common mistake in recreational running is doing nearly every session at a moderately hard effort — quick enough to hurt, not quick enough to drive adaptation, and too hard to recover from properly.
The pattern that works is a large volume of genuinely easy running, where you could hold a conversation, plus a small proportion of properly hard work. Theheart rate zones give you a way to keep the easy days honest, which is harder than it sounds.
Treadmill and terrain
Treadmill pace flatters you. There is no air resistance, no wind and no gradient variation, and the belt does some of the work of bringing the ground back. Setting one percent incline is the usual correction.
Hills, heat and trail surfaces all move real pace substantially at the same effort. Comparing paces across those conditions tells you about the conditions, not about your fitness.
Common questions
How do you calculate running pace?
Divide your total time by the distance covered. A 25-minute 5K is 1,500 seconds over 5 km, which is 300 seconds — five minutes — per kilometre. Pace is time per unit distance; speed is distance per unit time. Runners use pace because it is the number you can hold in your head mid-race.
How do I predict a race time from another distance?
Riegel's formula scales a known result: predicted time = known time × (new distance ÷ known distance) raised to the power 1.06. The exponent above 1 encodes the fact that pace degrades as distance grows. It holds reasonably from about 1500 m to the marathon.
How accurate are race time predictions?
Good between adjacent distances, optimistic for big jumps. Predicting a 10K from a 5K is usually within a couple of percent. Predicting a marathon from a 5K assumes you have done the endurance training a marathon requires — the formula cannot know whether you have, and will flatter you if you have not.
What is a good 5K time?
For a recreational adult runner, under 30 minutes is a solid starting benchmark, under 25 is respectable and under 20 is genuinely quick. Age and sex shift all of those substantially, and the more useful comparison is against your own previous times.
Should I train at my race pace?
Only for a small part of your week. Most running volume should be considerably slower than race pace — easy enough to hold a conversation — with a small amount of work at or faster than target pace. Training mostly at race pace is the classic way to plateau and accumulate fatigue.
Why is my treadmill pace easier than outdoors?
No air resistance, a surface that partly comes to you, and no gradient changes or wind. Setting a treadmill to one percent incline is the usual adjustment to approximate outdoor effort at the same pace.