About the Running Pace Calculator
This running pace calculator works out your pace per kilometre or mile and your average speed from a distance and finish time, then uses that effort level to predict what you would run for other common race distances — 5K, 10K, half marathon and marathon. The predictions use Riegel's formula, the same endurance-adjusted model race coaches and training plans commonly rely on, rather than a naive straight-line scaling that overstates what a longer distance actually costs.
How to use the Running Pace Calculator
- 1
Enter the distance you ran or plan to run, in kilometres or miles.
- 2
Enter your finish time, or a goal time, in hours and minutes.
- 3
Read your pace per unit distance and your average speed.
- 4
Check the predicted times table to see what the same effort level would produce over other common race distances.
What people use it for
Setting a goal pace for race day
Work out exactly what pace per kilometre or mile a target finish time requires, so it can be checked against a GPS watch during the race.
Choosing a realistic race distance
Use a recent training run's pace to see a realistic predicted time for an upcoming 10K or half marathon before committing to a goal.
Tracking improvement over time
Compare pace from the same route run weeks apart to see genuine, measurable progress rather than relying on how a run felt.
Riegel's formula, and why longer races take proportionally more time
Riegel's formula predicts a time for a new distance by taking a known time and multiplying it by the ratio of the two distances raised to the power of 1.06, an exponent derived from analysing large numbers of real race results across distances. Because the exponent is slightly above 1, doubling the distance more than doubles the predicted time — a runner who covers a 5K at a certain pace will run their 10K somewhat slower per kilometre, reflecting the real physiological cost of sustaining effort over a longer duration, rather than assuming pace holds perfectly flat.
Why predictions get less reliable over a bigger distance jump
Riegel's formula assumes broadly similar training and pacing discipline behind both distances, which holds reasonably well between distances that are physiologically similar, such as 10K to half marathon. Predicting a marathon time from a 5K result stretches that assumption much further, since marathon performance depends heavily on endurance-specific training — fuelling strategy, long runs, fatigue resistance — that a fast short-distance time says very little about. Treat a marathon prediction from a short race as an optimistic upper bound rather than a reliable target.
Tips
- Use a recent, honestly-paced race or time trial rather than a single best-ever effort for the most realistic predictions.
- Predictions between similar distances are far more trustworthy than a big jump, such as 5K to marathon.
- Pace naturally varies with terrain and weather — compare like-for-like routes and conditions when tracking progress over time.