How length conversion works
Every unit in the converter is defined as an exact number of metres. To convert, the calculator multiplies by the size of the unit you start with and divides by the size of the unit you want.
Imperial and US units have been tied to the metric system since 1959, when the United States, the United Kingdom and other Commonwealth countries agreed on the international yard and pound. That agreement fixed the inch at exactly 2.54 cm, so conversions such as inches to centimetres are exact, not approximations.
Key factors
| Unit | In metric | Exact? |
|---|---|---|
| 1 inch | 2.54 cm | Yes |
| 1 foot (12 in) | 30.48 cm | Yes |
| 1 yard (3 ft) | 0.9144 m | Yes |
| 1 mile (1,760 yd) | 1.609344 km | Yes |
| 1 nautical mile | 1,852 m | Yes |
| 1 thou (mil) | 0.0254 mm | Yes |
| 1 gaz | 0.9144 m (36 in) | Modern usage |
| 1 girah | 5.715 cm (2.25 in) | Traditional |
| 1 karam | 1.6764 m (5.5 ft) | Punjab land records |
Going the other way, 1 cm is about 0.3937 inches, 1 m is about 3.2808 feet and 1 km is about 0.6214 miles. Those reverse figures never end in decimals, which is why the converter shows up to 10 significant digits by default; choose fewer decimals for everyday use.
Worked examples
- Height: 5 ft 9 in = 5 × 12 + 9 = 69 inches. 69 × 2.54 = 175.26 cm.
- Screen size: a 15.6-inch laptop screen is 15.6 × 2.54 = 39.62 cm across the diagonal.
- Running: a 10 km race is 10 ÷ 1.609344 = 6.21 miles; a marathon of 26.2 miles is about 42.16 km.
- Fabric: 2.5 gaz of cloth is 2.5 × 36 = 90 inches, or 2.286 m.
South Asian units
In Pakistan and India, lengths in shops and on building sites are often given in traditional units:
- Gaz is the everyday word for a yard. Cloth is still sold by the gaz, and in modern use it is exactly 36 inches. Historic gaz varied from region to region, from roughly 24 to 41 inches, so old documents may use a different value.
- Girah is one sixteenth of a gaz, 2.25 inches. Tailors use it for cloth widths and lengths.
- Karam (karm) is 5.5 feet and appears in Punjab land records. A square karam, also called a sarsahi, is 30.25 square feet, and nine of them make a marla of 272.25 square feet. Marla, kanal and bigha are units of area, not length.
Distances such as the kos and the cubit-like haath varied too much by period and place to convert reliably, so they are not included.
Tips
- Type in either box. Both sides are live, so you can enter centimetres and read inches, or the other way round.
- Swap reverses the units and keeps your number.
- Every unit at once: the panel at the bottom lists your value in all units. Click any line to make it the “To” unit.
- US survey foot: older US land surveys used a survey foot of 1200/3937 m, about 2 parts per million longer than the international foot. The US retired it at the end of 2022, and this converter uses the international foot.
For body measurements, the BMI calculator accepts feet and inches directly. To convert kilograms, pounds, stone or tola, use the weight converter, and for litres, cups and gallons use the volume converter.