Length unit conversion
Conversion factors defined by international agreement are exact; values rounded for everyday use may differ slightly.
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| From | To | Multiply by |
|---|---|---|
| 1 meter (m) | centimeters (cm) | 100 |
| 1 meter (m) | millimeters (mm) | 1000 |
| 1 kilometer (km) | meters (m) | 1000 |
| 1 kilometer (km) | miles (mi) | 0.621371 |
| 1 mile (mi) | kilometers (km) | 1.609344 |
| 1 mile (mi) | feet (ft) | 5280 |
| 1 foot (ft) | inches (in) | 12 |
| 1 foot (ft) | meters (m) | 0.3048 |
| 1 inch (in) | centimeters (cm) | 2.54 |
| 1 inch (in) | millimeters (mm) | 25.4 |
| 1 yard (yd) | feet (ft) | 3 |
| 1 yard (yd) | meters (m) | 0.9144 |
| 1 nautical mile | kilometers (km) | 1.852 |
| 1 nautical mile | miles (mi) | 1.15078 |
| 1 centimeter (cm) | inches (in) | 0.393701 |
Notes
- International inch is exactly 25.4 mm.
- Nautical mile is defined as exactly 1852 m.
Why length conversion is pure multiplication
Length scales start at a true zero, so converting between them is a single multiplication — no offsets, unlike temperature. A few anchors are exact by international agreement: 1 inch = 2.54 centimeters exactly, which fixes the foot at 0.3048 m and the yard at 0.9144 m. The mile is defined as 5280 feet, so 1 mi = 1609.344 m exactly, and 0.621371 is simply 1 ÷ 1.609344. Chains work by multiplying factors along the way: to turn 63,360 inches into miles, divide by 12 to get 5280 feet, then divide by 5280 to get exactly 1 mile. Because every factor is exact, the only rounding in your answer is the rounding you choose to apply at the end.
Common mistakes to avoid
The most frequent error is direction: multiplying by a factor when you should divide by it (or multiply by its reciprocal). Check units as you go — if inches are supposed to become feet, the number must shrink. Another classic is mixing up 1 km ≈ 0.62 mi with 1 mi ≈ 1.6 km; remember a mile is the longer unit, so a mile count is always smaller than a kilometer count for the same distance. In multi-step chains, don't round 2.54 or 1.609344 too early — rounding at each step compounds the error. Finally, never use statute-mile factors for nautical miles: 1 nmi = 1.852 km (and ≈ 1.15078 statute miles), the standard in aviation and marine navigation.
Practical reference points worth memorizing
A handful of anchors covers most daily needs. 1 inch = 2.54 cm describes screens, tools, and hardware sizes. A person who is 6 feet tall is about 183 cm. Driving at 60 mph is roughly 96.5 km/h — about 1.6 km every minute — which makes speed conversion easy to sanity-check. A 5K run is 3.11 miles, and race distances between 5K and marathon are handy rulers for longer distances. Going the other way, 1 cm ≈ 0.3937 in, so 10 cm is just under 4 inches. With 2.54, 1.6, 0.62, and 0.9144 in your head, you can estimate any everyday length within a few percent before reaching for a calculator.
Regional and standard differences
Metric units are official almost everywhere, but the details matter. The United States uses miles, feet, and inches on road signs and in daily life; the UK mixes metric measures with informal miles and feet. Technically, the US now uses the international foot of exactly 0.3048 m — the older US survey foot (1200/3937 m) is obsolete for most purposes, though it lingers in old land records. The nautical mile is the easiest case: exactly 1852 m worldwide by international agreement, used for sea and air navigation. Aviation globally reports altitude in feet and distances in nautical miles, so even fully metric countries encounter imperial-derived units in flight — one more reason to keep these factors straight.
Frequently asked questions
- How many feet are in one mile?
- One mile equals exactly 5,280 feet, which is about 1.609 kilometers.
- How many centimeters are in an inch?
- One inch is exactly 2.54 cm, so 1 cm ≈ 0.3937 inches.
- How many kilometers are in a mile?
- One mile is exactly 1.609344 km; conversely, 1 km ≈ 0.621371 miles.