Length Converter

How it works

Every unit here is defined as an exact number of metres. The metric units are powers of ten apart. The US customary units have been defined in metric terms since the international yard and pound agreement of 1959: one yard is exactly 0.9144 m, which makes one inch exactly 25.4 mm, one foot exactly 0.3048 m and one mile exactly 1,609.344 m. The nautical mile, used at sea and in the air, is defined directly as 1,852 m.

The calculator multiplies your value by the size of the from unit in metres, then divides by the size of the to unit. The factor shown is what one from unit equals in the to unit, so you can repeat the conversion by hand or in a spreadsheet.

Because the definitions are exact, conversions between inches, feet, yards and miles come out as exact whole numbers (12 inches to the foot, 5,280 feet to the mile), and conversions to metric are exact decimals. Results are rounded to six decimal places for display only.

Formula

metres = value × metres per from unit
result = metres ÷ metres per to unit
factor = metres per from unit ÷ metres per to unit
1 in = 25.4 mm   1 ft = 0.3048 m   1 yd = 0.9144 m   1 mi = 1,609.344 m   1 nmi = 1,852 m   (exact)

Example

The default, 1 inch to centimetres: 1 × 0.0254 m ÷ 0.01 m = 2.54 cm. The factor is 2.54 cm per inch.

1 mile to kilometres is 1,609.344 m ÷ 1,000 m = 1.609344 km, and the same mile is 5,280 feet. 100 m to yards is 100 ÷ 0.9144 = 109.361330 yd. 1 nautical mile is 1.852 km, or 1,852 ÷ 1,609.344 = 1.150779 statute miles.

Assumptions and limitations

• Units use the exact legal definitions from the 1959 international yard and pound agreement (1 yd = 0.9144 m) and the SI, as tabulated in NIST Special Publication 811, Appendix B.
• The mile is the international (statute) mile of 5,280 ft and the nautical mile is the international nautical mile of 1,852 m. The US survey foot (1200/3937 m, about 2 parts per million longer) is not included.
• A negative value converts with its sign kept, so a change in length can be converted as well as a length.
• Results are rounded to six decimal places for display; the arithmetic is done in full double precision.

Frequently asked questions