Length Converter
Convert a distance between millimeters, centimeters, meters, kilometers, inches, feet, yards and miles using exact definitions.
Common Lengths
Length Conversion Facts
• 1 meter = 3.28084 feet = 39.3701 inches
• 1 kilometer = 0.621371 miles = 3,280.84 feet
• 1 inch = 2.54 centimeters (exact)
• 1 foot = 12 inches = 30.48 centimeters
• 1 yard = 3 feet = 0.9144 meters
Updated Formula covered by automated tests
Type a distance in millimeters, centimeters, meters, kilometers, inches, feet, yards or miles and the converter shows the same distance in all the other units at once. It is built for the everyday moments when two measuring systems meet: a furniture listing in centimeters for a room you measured in feet, a running route planned in kilometers on an app set to miles, or a technical drawing in millimeters that has to be cut on an imperial saw.
Every imperial length here is tied to the meter by an exact number, not a rounded estimate. That matters more than it seems. Rounding a mile to 1.6 km loses 9.3 meters per mile, which adds up to almost 2 km over a 200-mile drive, and rounding an inch to 2.5 cm puts a 72-inch shelf off by more than 2.8 cm.
The formula
- meters per source unit
- How many meters one of the units you typed is worth, for example 0.3048 for feet
- meters per target unit
- How many meters one of the units you want is worth, for example 1609.344 for miles
- 0.0254 m
- The international inch, which every other US customary length unit is built from
The converter routes every value through the meter. Your input is multiplied by its meter value, then divided by the meter value of each target unit. Using a single base unit means there is only one number per unit to get right, and any pair of units converts consistently in both directions.
The exact figures come from the international yard and pound agreement of 1959, in which the United States, the United Kingdom, Canada, Australia, New Zealand and South Africa agreed that one yard is exactly 0.9144 meters. From that, the foot is a third of a yard (0.3048 m), the inch is a twelfth of a foot (2.54 cm), and the statute mile of 5,280 feet works out to exactly 1,609.344 meters. The meter itself has been defined since 1983 by the distance light travels in a vacuum in 1/299,792,458 of a second.
Worked example
Priya has entered a half marathon advertised as 21.0975 km, but her running watch reports distance in miles and she wants to know what to expect on the display at the finish line and how many feet that is.
- 1 Convert kilometers to meters: 21.0975 × 1000 = 21,097.5 m.
- 2 Divide by the meters in one mile: 21,097.5 ÷ 1609.344 = 13.1094 mi.
- 3 For feet, divide the meters by 0.3048: 21,097.5 ÷ 0.3048 = 69,217.5 ft.
- 4 Check the two answers agree: 13.1094 × 5,280 = 69,217.6 ft, matching to within rounding.
Result: The half marathon is 13.11 miles (about 69,218 feet). If Priya’s watch shows 13.2 or 13.3 miles at the end, the extra comes from GPS error and not running the shortest line through bends, not from the conversion.
Before you rely on the result
- Results are exact arithmetic on the numbers entered; they cannot add accuracy that the original measurement lacked.
- Statute miles only: nautical miles, the US survey foot and historical units such as the furlong, rod or chain are not included.
- Very large and very small values are shown in scientific notation, so read the exponent before copying a result.
Frequently asked questions
Why does my old survey map use a slightly different foot?
Until the end of 2022 the United States also used the US survey foot, defined as 1200/3937 meters (about 0.3048006 m), for land surveying and state plane coordinates. It differs from the international foot by 2 parts per million, which is only about 3.2 mm per mile but becomes noticeable over large coordinate values. NIST and NOAA retired it for new work from January 1, 2023, so most users only meet it on older deeds and maps.
How do I convert a height like 5 ft 9 in to centimeters?
Turn it into inches first: 5 × 12 + 9 = 69 inches. Then multiply by 2.54 to get 175.26 cm. Going the other way, divide centimeters by 2.54 to get total inches, then divide by 12 for the feet and keep the remainder as inches.
Is a nautical mile the same as a mile?
No. A nautical mile is exactly 1,852 meters, about 15 percent longer than the 1,609.344-meter statute mile used on road signs. It is used at sea and in aviation because one nautical mile is close to one minute of latitude. This converter uses statute miles; the speed converter covers knots, which are nautical miles per hour.
How many decimal places should I keep?
Keep one or two more significant figures than your original measurement had, then round at the end. A tape reading of 182 cm converts to 71.65 inches, but quoting 71.6535 inches suggests a precision the tape never had.
Sources
- NIST: Unit conversion (SI and US customary units) (nist.gov)
- NIST: The US survey foot (nist.gov)
- BIPM: The International System of Units (SI Brochure) (bipm.org)