Pace Calculator
Convert between running pace, speed, distance, and finish time — with per-kilometre splits and predicted times for every standard race distance.
How to use this calculator
- 1Enter the distance you ran and pick kilometres or miles.
- 2Enter your finish time in hours, minutes, and seconds.
- 3Read your pace in both unit systems, plus your speed.
- 4Use the prediction table to set realistic targets at other race distances.
How it works
Pace, speed, and race prediction
pace = time ÷ distance speed = distance ÷ time 1 mile = 1.609344 km Riegel: T₂ = T₁ × (D₂ ÷ D₁)^1.06
Pace and speed are reciprocals of each other — pace tells you time per unit of distance, speed tells you distance per unit of time. Riegel's formula predicts across distances using an exponent slightly above 1, which encodes the fact that you cannot hold a 5K pace for a marathon: doubling the distance costs more than doubling the time.
Worked example
Running 10 km in 52 minutes 30 seconds is a pace of 5:15 per kilometre, or 8:27 per mile — a speed of 11.43 km/h. Riegel predicts a half marathon at around 1:55:30 and a marathon at about 4:00:50.
Pace Calculator: the complete guide
Pace versus speed
Runners think in pace — minutes per kilometre or per mile — because it maps directly onto a watch and onto a race plan. Cyclists and treadmills think in speed, because it maps onto a display and onto gearing. They are the same information inverted.
The counterintuitive part is that lower is better for pace and higher is better for speed. A 5:00/km pace is faster than 5:30/km, while 12 km/h is faster than 11 km/h. Mixing the two is how people accidentally set a treadmill three minutes per mile too fast.
How reliable are race predictions?
Riegel's formula works well when the two distances are within a factor of about four and you have trained for the target. A 10K time predicts a half marathon reliably. A 5K time predicting a marathon is a much longer extrapolation, and it assumes an endurance base you may not have built.
The exponent of 1.06 encodes how much you slow down as distance grows. Well-trained marathoners sometimes beat it with an effective exponent nearer 1.05; runners whose long runs are short relative to the race often land at 1.07 or worse. If your predicted marathon time feels too good, it probably is — the gap is usually training volume, not talent.
Even splits, negative splits, and the marathon wall
The split table above assumes perfectly even pacing, which is close to optimal for most distances and almost never what happens in practice. Adrenaline and fresh legs make the first mile the easiest to run too fast, and every second banked early is repaid with interest later.
A negative split — running the second half slightly faster than the first — is how most personal bests are actually set. Aim to run the first half 1–2% slower than target pace and let the second half come to you.
The marathon wall around 32 km is a glycogen problem, not a willpower problem. Muscle glycogen stores are good for roughly 30 km at race pace, which is why fuelling early and often, rather than waiting until you feel empty, is the single highest-return change most first-time marathoners can make.
Frequently asked questions
What is a good running pace for a beginner?
Most new runners settle somewhere between 6:00 and 8:00 per kilometre (roughly 10:00 to 13:00 per mile) for easy runs. Far more important than the number is being able to hold a conversation while running — if you cannot, you are running your easy days too hard.
How do I convert min/km to min/mile?
Multiply by 1.609344. A 5:00/km pace is 5 × 1.609344 = 8.05 minutes, or 8:03 per mile. This calculator shows both simultaneously so there is nothing to convert by hand.
What pace do I need to break 4 hours in a marathon?
About 5:41 per kilometre, or 9:09 per mile, held for the full 42.195 km. Enter 42.195 km and a 4:00:00 time above to see the exact splits, then check the prediction table from a recent 10K to see whether that target is realistic.
Why are my predicted longer-distance times slower than expected?
Because endurance does not scale linearly. Riegel's exponent of 1.06 means doubling the distance costs about 7% more than double the time. That is an empirical fit across thousands of race results, and it holds up remarkably well for trained runners.