How Long Is a 5K, 10K, Half Marathon, and Marathon in Miles?
Official road race distances in kilometers and miles, why a marathon is 26.2 miles, how courses are measured, and finish times at common beginner paces.
Race names mix units in a way that confuses new runners: a "5K" is measured in kilometers, but in the US most people think in miles. And why is a marathon such an odd number? World Athletics, the global governing body for running, sets the official distances and how courses are measured. Here is what each one works out to, plus what those distances mean in time at a beginner's pace.
The official standard distances
World Athletics' Technical Rules list the standard road race distances as 5 km, 10 km, 15 km, 20 km, half marathon, 25 km, 30 km, marathon (42.195 km), 100 km, and road relay.
Converted to miles, using the international definition of 1 mile = 1.609344 km:
| Race | Kilometers | Miles (rounded) |
|---|---|---|
| 5K | 5 | 3.107 |
| 10K | 10 | 6.214 |
| 15K | 15 | 9.321 |
| Half marathon | 21.0975 | 13.109 |
| Marathon | 42.195 | 26.219 |
That is why a 5K is often called "3.1 miles," a half marathon "13.1," and a marathon "26.2." World Athletics' own half marathon page gives the figure as 13.1094 miles, exactly half a marathon.
Why the marathon is 42.195 km
World Athletics explains the history on its marathon page. The organizers of the first modern Olympic Games, in Athens in 1896, created the marathon over about 40 km to celebrate ancient Greece. At the 1908 London Olympics, the distance was extended to 26 miles, then another 385 yards were added when the start was moved so it could be seen from the Royal Nursery at Windsor while still finishing in front of Queen Alexandra at the White City Stadium in London. The distance was standardized at 26 miles 385 yards (42.195 km) in 1921.
The math checks out: 385 yards is 0.21875 of a mile, so the marathon is 26.21875 miles, which rounds to the familiar 26.2.
How courses are measured
A race's distance is not just a number on a sign. Under World Athletics' rules:
- The course is measured along the shortest possible route a runner could take within the part of the road allowed for the race.
- The course must not be shorter than the official distance.
- For major international competitions, the measurement uncertainty must not exceed 0.1%, which World Athletics notes is 42 meters for the marathon.
- Measurement uses the calibrated bicycle method, and measurers are advised to build in a short-course prevention factor of 0.1%, so each kilometer is laid out as 1,001 meters.
These rules are one reason a watch reading at the finish may not match the race distance exactly: the official figure is based on the shortest legal line through the course, and the course is laid out slightly long rather than short.
Finish times at common paces
For planning, here is how long each distance takes at a steady pace. These are straightforward calculations from the mile distances above, not predictions:
| Race | 10 min per mile | 12 min per mile | 15 min per mile |
|---|---|---|---|
| 5K | about 31 min | about 37 min | about 47 min |
| 10K | about 1 h 02 min | about 1 h 15 min | about 1 h 33 min |
| Half marathon | about 2 h 11 min | about 2 h 37 min | about 3 h 17 min |
| Marathon | about 4 h 22 min | about 5 h 15 min | about 6 h 33 min |
A 15-minute mile is 4 mph, the top of the 2.5 to 4 mph range the federal Physical Activity Guidelines give for brisk walking. So the slowest column is roughly what a fast walk would produce.
Choosing a first race
World Athletics' half marathon page offers some general guidance for people working up to that distance, including training for a minimum of 12 weeks, increasing distance gradually, resting between sessions, and always doing warm-up and cool-down activities. For most beginners, a 5K or 10K is the natural first step before any of that.
If you sign up for an event, check the race's own rules for time limits, since a 15-minute-per-mile half marathon takes over three hours.
Key takeaways
- World Athletics' standard road distances include 5 km, 10 km, 15 km, 20 km, the half marathon, and the marathon at 42.195 km.
- A 5K is 3.107 miles, a 10K is 6.214 miles, a half marathon is 13.109 miles, and a marathon is 26.219 miles.
- The marathon was fixed at 26 miles 385 yards in 1921, after the 1908 London Olympics.
- Courses are measured on the shortest possible route and may not be shorter than the official distance.
- At 12 minutes per mile, a 5K takes about 37 minutes and a 10K about 1 hour 15 minutes.
This article is general information, not medical advice. Talk with a doctor before starting a new exercise routine, especially if you have a health condition.