The short answer
1 kilometer = 0.6213711922 miles. Multiply kilometers by 0.621371.
miles = kilometers × 0.6213711922
kilometers = miles × 1.609344The mile is exactly 1609.344 meters by definition, following from the exact inch.
The Fibonacci trick
Consecutive Fibonacci numbers (1, 2, 3, 5, 8, 13, 21, 34, 55, 89) have a ratio approaching 1.618 — remarkably close to 1.609. So a Fibonacci number in kilometers is roughly the next one down in miles:
- 5 km ≈ 3 mi (true 3.107)
- 8 km ≈ 5 mi (true 4.971)
- 13 km ≈ 8 mi (true 8.078)
- 89 km ≈ 55 mi (true 55.3)
For non-Fibonacci values, decompose: 70 km = 55 + 13 + 2 → 34 + 8 + 1 = 43 mi (true 43.5).
Simpler alternative: multiply by 6 and drop a digit, then add 3%. 40 km → 24, +3% ≈ 24.9 mi (true 24.85).
Running distances
| Race | Kilometers | Miles |
|---|---|---|
| 5K | 5 km | 3.107 mi |
| 10K | 10 km | 6.214 mi |
| Half marathon | 21.0975 km | 13.109 mi |
| Marathon | 42.195 km | 26.219 mi |
| 50K ultra | 50 km | 31.069 mi |
| 100 mile | 160.934 km | 100 mi |
Pace converts inversely: 5:00 min/km = 8:03 min/mile; 8:00 min/mile = 4:58 min/km.
Speed limits
| km/h | mph |
|---|---|
| 30 | 18.6 |
| 50 | 31.1 |
| 60 | 37.3 |
| 80 | 49.7 |
| 100 | 62.1 |
| 120 | 74.6 |
| 130 | 80.8 |
Enforcement is on the posted unit — a US car showing 62 mph in a 100 km/h zone is exactly at the limit, not under it.
Miles that are not the mile
| Unit | Meters | Use |
|---|---|---|
| Statute mile | 1609.344 | Roads |
| Nautical mile | 1852 | Sea, air |
| US survey mile | 1609.347 | Legacy land records |
| Scandinavian mil | 10,000 | Informal, Norway/Sweden |
The nautical mile is one minute of latitude, which is why it is 1852 m exactly (international definition, 1929) and why one knot = one nautical mile per hour = 1.852 km/h.
Key takeaways
- 1 mi = 1609.344 m exactly; km × 0.621371 = mi
- Fibonacci pairs give fast, surprisingly accurate mental conversions
- Nautical miles (1852 m) are 15% longer than statute miles
- Pace and fuel figures convert inversely, not by the same factor