Length Converter (m, ft, in, yd)

Understanding the length converter — concept and principle

Length is the most common conversion people need: a height in feet and inches, a room in metres, a screen in inches, a road distance in miles or kilometres. This converter changes a value between metres, centimetres, millimetres, kilometres, inches, feet, yards and miles, and lists the value in every unit at once.

How it is calculated

The value is first converted into metres, then into the unit you pick:

• 1 cm = 0.01 m; 1 mm = 0.001 m; 1 km = 1,000 m
• 1 in = 0.0254 m; 1 ft = 12 in = 0.3048 m
• 1 yd = 3 ft = 0.9144 m; 1 mi = 1,760 yd = 1,609.344 m

Result = value × (metres in source unit) ÷ (metres in target unit). Results are shown to 10 significant digits.

The principle

The metre is the SI base unit of length, defined since 1983 by the distance light travels in a vacuum in 1/299,792,458 of a second. Customary units are defined from it: under the international yard and pound agreement of 1959, the yard became exactly 0.9144 m, which makes the foot exactly 0.3048 m and the inch exactly 2.54 cm. Because every factor is exact, a conversion only loses precision through rounding of the displayed result. Converting through one base unit also means you never need a separate table for every pair of units.

Worked example

1. Default inputs: value 6, from feet, to metres.
2. 6 × 0.3048 = 1.8288 m.
3. Other units: 182.88 cm, 1,828.8 mm, 0.0018288 km, 6 × 12 = 72 in, 6 ÷ 3 = 2 yd and 6 ÷ 5,280 ≈ 0.0011363636 mi.

How to read the result

6 ft (about 183 cm) is a common reference height. For quick mental conversions: 1 m ≈ 3.28 ft ≈ 39.37 in, 1 km ≈ 0.621 mi and 1 mi ≈ 1.609 km. A height written as 5 ft 9 in must be converted as 5 × 30.48 + 9 × 2.54 = 175.26 cm, not by entering 5.9 ft. The calculator shows many digits; round to the precision of your original measurement.

Common mistakes

• Entering 5'9" as 5.9 ft. 5 ft 9 in is 5.75 ft.
• Confusing the statute mile (1,609.344 m) with the nautical mile (1,852 m).
• Converting area or volume with length factors; square and cubic units need the factor squared or cubed.

Frequently asked questions

How many feet are in a metre?

1 m = 3.280839895 ft (1 ÷ 0.3048).

How many centimetres is an inch?

Exactly 2.54 cm.

How tall is 6 ft in cm?

182.88 cm, usually given as 183 cm.

How do I convert 170 cm to feet and inches?

170 ÷ 2.54 = 66.93 in; 66.93 ÷ 12 = 5 ft with 6.93 in left, so about 5 ft 7 in.

Sources: BIPM, The International System of Units (SI Brochure), 9th edition, 2019 · NIST Special Publication 811 (2008), Appendix B