A 5K is 3.1069 miles, a 10K is 6.2137 miles, a half marathon is 13.1094 miles and a marathon is 26.2188 miles. Pace goes the other way: a minutes-per-kilometre figure is multiplied by 1.609344 to get minutes per mile, so 5:00/km is 8:03/mi — a bigger number for the same speed, because a mile takes longer than a kilometre.
That inversion is what makes pace conversion feel wrong. Distances get smaller going from kilometres to miles and paces get larger, and both are correct.
What are the standard distances in both units?
The metric figures are the definitions. Road race distances are set in metres by World Athletics, and the mile equivalents are conversions of them rather than the other way round.
| Race | Kilometres | Miles |
|---|---|---|
| Mile | 1.609344 | 1 |
| 5K | 5 | 3.1069 |
| 10K | 10 | 6.2137 |
| Half marathon | 21.0975 | 13.1094 |
| Marathon | 42.195 | 26.2188 |
The marathon is the one people round hardest. It is 26.2188 miles, not 26.2 — a difference of about 30 metres, which sounds trivial until it is the 30 metres between you and a target time.
How do you convert a pace?
Multiply minutes per kilometre by 1.609344 to get minutes per mile, and divide to go the other way. The decimal result then needs turning back into minutes and seconds: 5.0 min/km × 1.609344 is 8.047 min/mi, and 0.047 of a minute is 3 seconds, giving 8:03.
| Per kilometre | Per mile | km/h | mph |
|---|---|---|---|
| 4:00 | 6:26 | 15.00 | 9.32 |
| 4:30 | 7:15 | 13.33 | 8.28 |
| 5:00 | 8:03 | 12.00 | 7.46 |
| 5:30 | 8:51 | 10.91 | 6.78 |
| 6:00 | 9:39 | 10.00 | 6.21 |
| 6:30 | 10:28 | 9.23 | 5.74 |
| 7:00 | 11:16 | 8.57 | 5.33 |
Why does the watch disagree with the mile markers?
Because a GPS watch measures the path you ran and the course measures the shortest legal route around it. Race distances are certified along the tangents — the inside line through every bend — and nobody runs that line for 42 kilometres.
A watch reading 42.4 km on a certified marathon is not broken and the course is not long. You ran 200 metres further than the measured route, which at 5:00/km is a minute you did not plan for. The fix is to run tangents deliberately and to pace off the course markers rather than off the watch.
What is a useful mental shortcut?
Consecutive Fibonacci numbers approximate kilometre-to-mile pairs, because the golden ratio of 1.618 is within half a per cent of 1.609344. Five kilometres is about three miles, eight is about five, thirteen is about eight, twenty-one is about thirteen.
That last pair is why the half marathon is 21 km and 13 miles. The trick holds well to around 100, where accumulated error passes a mile and a half and it stops being useful.
How do treadmill speeds convert?
A treadmill shows speed rather than pace, so it needs two steps: convert the unit, then invert it. A belt at 12.0 km/h is 7.46 mph, and both are 5:00 per kilometre or 8:03 per mile. Sixty divided by the speed gives the pace, which is why a small change at the fast end of the dial moves the pace far less than the same change at the slow end.
Going from 8 to 9 km/h takes the pace from 7:30 to 6:40 per kilometre, a saving of 50 seconds. Going from 15 to 16 km/h takes it from 4:00 to 3:45, a saving of 15. The dial is linear and the pace is not.
What do the track distances convert to?
A standard outdoor lane-one lap is 400 m, which is 0.2485 miles, so four laps is 1,600 m or 0.9942 miles — not a mile. The mile is 1,609.344 m, which is 9.344 m further, or about a fifth of the home straight.
That gap is why a 1,600 m school time and a mile time are different events, and why converting one to the other by proportion flatters the runner slightly. Indoor tracks are usually 200 m and often banked, and the tighter bends make those times not directly comparable to outdoor ones at all.
Questions people ask
Is a 5K really 3.1 miles? It is 3.1069 miles. Rounding to 3.1 loses 11 metres, which does not matter for training and does for a personal best.
Why is a marathon 42.195 km? The distance was fixed after the 1908 London Olympics, where the course ran from Windsor Castle to the stadium. It was standardised at that length in 1921 and has not moved since.
Does the mile differ between countries? Not the one races use. The international mile is exactly 1,609.344 metres in both the UK and the US. Nautical miles are a different unit at 1,852 m and are not used on land.
Can I convert a race time directly? Only for the same race. A 5K time does not scale to a 10K by doubling, because pace falls with distance — which is what race-prediction tables model, and they are estimates rather than conversions.
Why do race results list a chip time and a gun time? The gun time starts when the race starts and the chip time when you cross the line, and in a field of thousands those can be several minutes apart. Neither is a conversion issue; both are reported in the same units, and the qualifying standard usually specifies which one counts.
How accurate is a certified course? Courses are measured to be at least the stated distance, never shorter, using a calibrated bicycle wheel along the shortest legal route. A certified marathon is 42.195 km or a little over, which is one more reason a watch reading long is normal.
Distances convert cleanly; paces invert. Kilometres to miles and miles to kilometres handle both directions, and if you are tracking weight alongside training, kilograms to pounds is next door.