Kilometre to Mile
Free instant kilometre to mile converter. 1 km = 0.621371 mi.
Common Kilometre to Mile values
| Kilometre (km) | Mile (mi) |
|---|---|
| 1 | 0.621371 |
| 5 | 3.10686 |
| 10 | 6.21371 |
| 25 | 15.5343 |
| 50 | 31.0686 |
| 100 | 62.1371 |
| 500 | 310.686 |
| 1000 | 621.371 |
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How does Kilometre to Mile conversion work?
Type a value in the Kilometre (km) field and the equivalent in Mile (mi) appears instantly to the right. The math uses the exact formula shown above — no rounding errors, no approximations beyond standard floating-point precision. Use the swap button to flip the units and see the inverse conversion.
Kilometre. A metric unit equal to 1,000 metres. About 0.62 miles. A typical brisk-walk pace covers a kilometre in 10–12 minutes.
Mile. The standard road-distance unit in the US and UK. Defined as exactly 1,609.344 metres since 1959.
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Conversion factors come from the official standard (NIST, BIPM, ISO definitions where applicable). Values are precise to standard floating-point limits.
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How it works — the formula
Linear: value_in_base = value × scale
For length, scale = metres per unit (e.g. 1 ft = 0.3048 m exactly)Every length unit is defined in terms of the metre, the SI base unit. Since 1959 the international yard and pound agreement fixed 1 yd = 0.9144 m exactly, which gives 1 ft = 0.3048 m and 1 in = 0.0254 m exactly. The metre itself is defined by the speed of light: the distance light travels in 1/299,792,458 second (CGPM 1983).
Worked examples
- Inputs:
- 5 ft = ? m
- Output:
- 5 × 0.3048 = 1.524 m exactly
- Inputs:
- 100 km = ? mi
- Output:
- 100 / 1.609344 ≈ 62.1371 mi
- Inputs:
- 10 in → cm → in
- Output:
- 10 × 2.54 = 25.4 cm; 25.4 / 2.54 = 10.0000 in (exact within IEEE 754)
Limitations
- Conversion factors between SI and US-customary are exact since the 1959 agreement; older "US survey foot" values differ by ~2 ppm and are deprecated as of 2023.
- Astronomical units (light-year, parsec) are convertible but rarely useful at terrestrial scale.
- Floating-point representation imposes a ~15-significant-digit ceiling on round-trip accuracy.
- Conversion factor of 1 nautical mile = 1,852 m exactly applies to the international nautical mile, not the rarely-used US/British nautical mile (1,853.184 m).
Length conversions are exact rational arithmetic for SI ↔ US-customary pairs; trailing-digit differences come from binary floating-point representation only.