Converting kilometers to miles is essential when driving in the US, UK or reading Anglo car, plane or boat specs. Here you have the exact formula, reference table, mental trick and the key distinction with the nautical mile.
Exact formula
1 km = 0.62137119223733 miles (statute)
1 mile = 1.609344 km (exact definition since 1959)
Conversions:
- km → mi:
miles = km × 0.621371 - mi → km:
km = miles × 1.609344
Reference table (km → statute miles)
| km | mi (exact) | mi (rounded) | Context |
|---|---|---|---|
| 1 | 0.6214 | 0.62 | — |
| 5 | 3.1069 | 3.11 | 5K run |
| 10 | 6.2137 | 6.21 | 10K run |
| 20 | 12.4274 | 12.4 | Half marathon ≈ 21.1 km |
| 42.195 | 26.2188 | 26.2 | Marathon |
| 50 | 31.0686 | 31.1 | 50K ultra |
| 100 | 62.1371 | 62.1 | — |
| 160.934 | 100.000 | 100 | 100 miles |
| 200 | 124.274 | 124.3 | — |
Common speed limits
| km/h | mph (exact) | mph (rounded) |
|---|---|---|
| 30 | 18.64 | 19 |
| 50 | 31.07 | 31 |
| 60 | 37.28 | 37 |
| 80 | 49.71 | 50 |
| 90 | 55.92 | 56 |
| 100 | 62.14 | 62 |
| 110 | 68.35 | 68 |
| 120 | 74.56 | 75 |
| 130 | 80.78 | 81 |
Mental trick: “Divide by 1.6”
mi ≈ km / 1.6 (equivalently: mi ≈ km × 0.625)
| km | Trick | Exact | Error |
|---|---|---|---|
| 50 | 31.25 | 31.07 | +0.6 % |
| 100 | 62.5 | 62.14 | +0.6 % |
| 120 | 75.0 | 74.56 | +0.6 % |
| 200 | 125.0 | 124.27 | +0.6 % |
Systematic error ~+0.6 % (slight overestimate). Perfect for driving: you see 120 km/h → ~75 mph mentally.
Nautical mile (important for sea/air)
| Unit | Exact definition | Use |
|---|---|---|
| Statute mile | 1.609344 km | Roads, land maps, US/UK |
| Nautical mile | 1.852 km (exact) | Maritime navigation, aviation, GPS |
| Knot | 1 nautical mile / hour | Ship/plane speed |
1 nautical mile = 1.15078 statute miles
1 knot = 1.852 km/h = 1.15078 mph
Don’t confuse them: a ship at 20 knots goes 37 km/h, not 32 km/h.
Yards and feet (additional reference)
| Unit | Exact equivalence |
|---|---|
| 1 mile | 1,760 yards = 5,280 feet |
| 1 yard | 0.9144 m (exact) = 3 feet |
| 1 foot | 0.3048 m (exact) = 12 inches |
| 1 inch | 2.54 cm (exact) |
Conclusion
- Exact: km × 0.621371 = miles.
- Mental (driving): km / 1.6 ≈ mph (error +0.6 %).
- Table: print the speed limit one for the dashboard.
- Watch out: nautical mile = 1.852 km (not 1.609) for sea/air.
- Tool: unit converter for any value.