Two systems of length
Most of the world measures length in metric units built on the meter: the millimeter, centimeter and kilometer are just the meter multiplied or divided by a power of ten. The United States still uses US customary units day to day: inches, feet, yards and miles. The two systems have been tied together exactly since 1959, when the inch was fixed at 2.54 centimeters. Every customary length therefore has an exact metric value, and switching between them is a single multiplication.
How to use this converter
Type a value in any field and all the other units update at once. You can type with a decimal point or a decimal comma, and you can start from any unit, for example a distance in miles or a thickness in millimeters. Each unit pair also has its own page with the formula, a worked example and a printable chart, linked below the converter.
The factors behind the conversions
Internally every value goes through the meter. An inch is 0.0254 m, a foot 0.3048 m, a yard 0.9144 m and a mile 1,609.344 m. A nautical mile is 1,852 m by international agreement. Metric prefixes follow the usual pattern: micro is a millionth, milli a thousandth, centi a hundredth, deci a tenth and kilo a thousand.
Handy reference points
- 1 inch = 2.54 cm, and 1 cm ≈ 0.3937 in
- 1 foot = 30.48 cm, and 1 meter ≈ 3.2808 ft
- 1 yard = 0.9144 m, and 1 meter ≈ 1.0936 yd
- 1 mile = 1.609344 km, and 1 km ≈ 0.6214 mi
- A marathon is 42.195 km, or about 26.22 miles
Mistakes to avoid
Decimal feet are not feet and inches: 5.5 ft is 5 ft 6 in, not 5 ft 5 in. Rounding too early is the other trap. When a length is used to compute an area or a volume, keep a few extra digits and round only the final result, since squaring or cubing a length also multiplies its rounding error.
Length units compared
| Unit | Symbol | In meters |
|---|---|---|
| Micrometer | µm | 0.000001 |
| Millimeter | mm | 0.001 |
| Centimeter | cm | 0.01 |
| Decimeter | dm | 0.1 |
| Meter | m | 1 |
| Kilometer | km | 1,000 |
| Inch | in | 0.0254 |
| Foot | ft | 0.3048 |
| Yard | yd | 0.9144 |
| Mile | mi | 1,609.34 |
| Nautical mile | nmi | 1,852 |
The units in detail
What is a micrometer?
The micrometer, often called a micron, is one millionth of a meter, or a thousandth of a millimeter. It is the scale of bacteria, fine dust and plastic wrap. Machinists use it for tight tolerances, and filter and particle sizes are rated in microns.
What is a millimeter?
The millimeter is one thousandth of a meter. It is the unit of engineering drawings, metric bolts and drill bits, camera focal lengths, jewelry and rainfall in most countries. In the US it shows up on tools, packaging and anything built to metric standards.
What is a centimeter?
The centimeter is one hundredth of a meter, about the width of a fingernail. Most of the world uses it for body height, clothing measurements and furniture sizes. An inch is exactly 2.54 cm, so a 6-foot person is about 183 cm tall.
What is a decimeter?
The decimeter is one tenth of a meter, or 10 cm. It is rarely used in conversation but common in school exercises and in volume work, because a cube one decimeter on each side holds exactly one liter.
What is a meter?
The meter is the SI base unit of length. Since 1983 it has been defined as the distance light travels in a vacuum in 1/299,792,458 of a second. It is a little longer than a yard: one meter is about 1.0936 yards or 3.2808 feet.
What is a kilometer?
The kilometer equals 1,000 meters. Most countries use it for road distances and speed limits in km/h, and runners know it from the 5K, 10K and the 42.195 km marathon. One kilometer is about 0.62 mile.
What is an inch?
The inch has been exactly 2.54 centimeters since the 1959 international yard and pound agreement, and 12 inches make a foot. It is the US unit for screen diagonals, lumber, pipe and tire sizes, rainfall and most short lengths.
What is a foot?
The foot equals 12 inches, exactly 0.3048 meter. Americans use it for height, room and lot dimensions and ceiling heights, and pilots worldwide give altitude in feet. Three feet make a yard and 5,280 feet make a mile.
What is a yard?
The yard equals 3 feet or 36 inches, exactly 0.9144 meter. It lives on in American football fields, golf distances, fabric sold by the yard and bulk landscaping materials, which are priced by the cubic yard.
What is a mile?
The statute mile equals 5,280 feet or 1,760 yards, exactly 1,609.344 meters. It is the unit of road distances and speed limits (mph) in the United States and the United Kingdom, and of the classic one-mile race.
What is a nautical mile?
The nautical mile is exactly 1,852 meters, close to one minute of latitude on the Earth's surface, which makes chart work easy. Ships and aircraft navigate in nautical miles, and one nautical mile per hour is a knot.