How this works
1 km ≈ 0.621371 miles (the reciprocal of the exact 1.609344 mi-to-km factor). Useful when reading European distance signs, planning trail runs in metric, or telling someone in the US how far you walked today. The calculator above shows the precise figure plus every other common length unit.
The formula
For mental conversion, multiply km by 0.6 — gives an estimate within ~3.5%. The "Fibonacci trick" runs in both directions: a Fibonacci number in km roughly equals the previous Fibonacci in miles. So 8 km ≈ 5 mi, 13 km ≈ 8 mi, 21 km ≈ 13 mi (within 1%).
Example calculation
- 1 km = 0.621 mi
- 5 km = 3.107 mi (a 5K race)
- 10 km = 6.214 mi
- 42.195 km = 26.22 mi (marathon)
Frequently asked questions
How long is a 5K in miles?
3.107 miles. The standard 5K, 10K, half marathon and marathon distances are all defined in metric (5/10/21.097/42.195 km), even though they're run worldwide — including in countries that otherwise use miles. So the "5K" name carries through and you just need the conversion when reading per-mile pace info.
Why don't the units share a clean conversion factor?
Because the kilometre and the mile were defined independently — the metre as a fraction of the Earth's meridian, the mile from medieval Roman pace measurements. They were only formally pinned to each other in 1959 when the international yard was fixed at 0.9144 m. The 1.609344 conversion you see is the consequence of two unrelated historical definitions colliding in modern law.