🏃 Pace Calculator
Calculate running pace per kilometer or mile, finish times, and split speeds.
Pace, speed and finish time, and how to plan a race around them
Pace is time per unit of distance, and speed is distance per unit of time. They describe the same thing from opposite ends, and runners think in pace because it is the number you can hold in your head while moving: 5:00 per kilometre is a rhythm, 12 km/h is an abstraction.
pace = time / distance speed = distance / time finish time = pace × distance
Pace to finish time
| Pace per km | 5K | 10K | Half marathon | Marathon |
|---|---|---|---|---|
| 4:00 | 20:00 | 40:00 | 1:24:24 | 2:48:49 |
| 4:30 | 22:30 | 45:00 | 1:34:57 | 3:09:55 |
| 5:00 | 25:00 | 50:00 | 1:45:31 | 3:31:02 |
| 5:30 | 27:30 | 55:00 | 1:56:04 | 3:52:08 |
| 6:00 | 30:00 | 1:00:00 | 2:06:38 | 4:13:15 |
| 7:00 | 35:00 | 1:10:00 | 2:27:44 | 4:55:27 |
A marathon is 42.195 km, not 42, and a half is 21.0975 km. The extra 195 metres costs about a minute at marathon pace, which is exactly the margin that decides whether a four-hour target is met.
Pacing a race
Even pacing, or a slightly negative split where the second half is marginally faster, produces the best times for almost everyone. The common failure is going out two to three per cent too fast in the first five kilometres, feeling comfortable because the race is fresh, and paying for it with a much larger slowdown later. In marathon running this is severe enough to have its own name.
A useful discipline: write your target splits on your wrist and treat the first 10 km as a speed limit, not a target. If you are ahead of schedule early, you are not banking time, you are borrowing it at a punitive rate.
Predicting a longer race from a shorter one
Riegel's formula, published in 1977, estimates a time at one distance from a known time at another:
T2 = T1 × (D2 / D1)1.06
A 22:30 5K predicts a 46:50 10K, a 1:43:43 half and a 3:36:19 marathon. The exponent of 1.06 encodes the fact that you slow down as distance rises. The prediction is reliable for distances within about a factor of four, and optimistic for the marathon unless you have done the endurance work, because the marathon punishes inadequate training in ways the formula cannot see.
Converting between miles and kilometres
One mile is 1.609 km, so to convert a per-mile pace to per-kilometre, divide by 1.609. An 8:00 mile is a 4:58 kilometre. Going the other way, multiply: a 5:00 kilometre is an 8:03 mile. The rough mental version is that a per-km pace is about 62% of the per-mile pace.
A worked example
A runner wants to break 1:50 for a half marathon. That is 6,600 seconds over 21.0975 km, so 312.8 seconds per km, or 5:13 per kilometre, which is 8:24 per mile. Planning a 5-second-per-km cushion in the first half means running 5:08 for the first 10 km and allowing 5:18 afterwards, which still lands at 1:49:40.
This page explains published formulas and population-level ranges. It is general information, not medical advice, and it cannot account for your individual health. Talk to a doctor or a registered dietitian before changing how you eat, train or treat a condition.
Frequently Asked Questions (FAQs)
What is a good 5K time?
It depends entirely on age, sex and training history. Broad reference points for recreational runners: under 30 minutes is a solid first goal, under 25 is well-trained for most amateurs, and under 20 is competitive at club level. Compare yourself to your own previous times rather than to anyone else's.
How do I convert pace between miles and kilometres?
Divide a per-mile pace by 1.609 to get per-kilometre, or multiply a per-kilometre pace by 1.609 to get per-mile. A 10:00 mile is a 6:13 kilometre; a 6:00 kilometre is a 9:39 mile.
What is a negative split?
Running the second half of a race faster than the first. It is how most distance records are set, because it avoids the disproportionate slowdown that follows going out too hard. Aiming for even pacing and ending slightly faster is the practical version for most runners.
How accurate is the race prediction formula?
Riegel's formula is good within about a factor of four in distance, so a 5K predicts a 10K or a half well. Marathon predictions from a 5K are usually optimistic by several minutes unless you have built the endurance base, because the marathon is limited by fuelling and durability rather than speed.
Should I run at race pace in training?
Only for a limited portion. Most endurance programmes put roughly 80% of volume at an easy conversational pace and 20% at or above race intensity. Running everything at a moderately hard pace is the most common training error, producing fatigue without the adaptations of either easy or hard work.
Why is my GPS distance different from the official course?
GPS error accumulates with turns, tall buildings and tree cover, and courses are measured along the shortest legal line while you run slightly wider. Most runners record a marathon as 42.4 to 42.6 km. That is why it is worth pacing by effort and course markers rather than purely by watch distance.