How is a marathon course measured?
Officials' detail · The event · 1 of 2A road course is measured along the shortest route a runner could follow within the part of the road open to the race. It may not be shorter than the stated distance. Measurers ride it with a calibrated bicycle and add one metre for every kilometre as a safety margin. A certificate lasts five years.
How it works
- The line measured: "The course shall be measured along the shortest possible route that an athlete could follow within the section of the road permitted for use in the race."
- Never short: "The length of the course shall not be less than the official distance for the event."
- The method: the calibrated bicycle method.
- The margin: a "short course prevention factor" of 0.1% is recommended, so that each kilometre of the course has a measured length of 1,001 m.
- How exact: at World Rankings Competitions the uncertainty may not exceed 0.1%, which is 42 m for the marathon.
- Who: at those competitions the course is measured and certified in advance by an international road course measurer.
- The painted line: at the top competitions the measurement line should be marked along the course in a colour that cannot be mistaken for other markings.
- Cones and barriers: if parts of the course will be marked out on race day with movable equipment, where it goes must be decided by the time of measurement and written into the report.
- How long it lasts: a measurement certificate is valid for five years. The course must then be measured again even if nothing has visibly changed.
Tricky cases
A runner's watch shows 42.6 km at the end of a marathon. Was the course too long?
No, not on that evidence. The course is measured along the shortest possible route, and a runner who takes wider lines round bends and other runners covers more ground.
Can a certified course be a few metres short?
No. The length may not be less than the official distance.
Does a course measured six years ago still count?
No. A certificate is valid for five years.
Is the painted line the route runners must follow?
No. It shows the measured route. Runners may run anywhere on the part of the road open to the race.
Why the rule exists
Measuring the shortest route guarantees that nobody can cover less than the distance, whichever line they take. The extra metre in every kilometre is insurance, so that a course does not turn out to be short if it is measured again after a fast time.
Where it differs
| Where | What changes | Source |
|---|---|---|
| World Athletics rules | As above | TR 55.3 |
| Race walking on the road | Measured in the same way | TR 54.11.2 |
| Records | The course must be measured by an "A" or "B" grade measurer and may be checked again afterwards | CR 31.21 |
| Smaller races | The painted line is asked for at the top competitions and "where possible" elsewhere | TR 55.3 |
From the rule book
World Athletics, Competition and Technical Rules, 2026 Edition, Technical Rule 55.3 with its notes. Checked 14 October 2026. Official document: World Athletics Competition and Technical Rules 2026 (PDF).