Length converter

Multiply by the size of the starting unit in meters, then divide by the size of the target unit in meters. Six feet to centimeters: 6 × 0.3048 = 1.8288 m, and 1.8288 ÷ 0.01 = 182.88 cm. Within the metric system the prefixes do the work: kilo is a thousand, centi a hundredth, milli a thousandth, micro a millionth and nano a billionth, so converting between them only moves the decimal point.

Since 1983 the meter has been the distance light travels in a vacuum in 1/299,792,458 of a second, a definition kept in the BIPM’s SI Brochure. Its first definition, in revolutionary France, was one ten-millionth of the distance from the North Pole to the equator through Paris. The surveyors Delambre and Méchain measured that arc between 1792 and 1798, and with the period’s limited knowledge of the Earth’s shape the result came out slightly short — which is why the real pole-to-equator distance is about 10,002 km instead of the round 10,000 the meter was meant to give.

It had two until recently. Alongside the international foot of 0.3048 m, American land surveys kept the older US survey foot of 1200/3937 m, about two parts per million longer. Over a few meters the difference is invisible; across a state-wide coordinate grid it adds up to meters. NIST and the National Geodetic Survey retired the survey foot at the end of 2022, so there is now one foot.

A statute mile is 5,280 feet, or 1,609.344 m. A nautical mile is 1,852 m, fixed at the International Hydrographic Conference in Monaco in 1929 to approximate one minute of latitude. Ships and aircraft use the nautical mile; roads use the statute mile. The most searched length conversions on this site are inches to cm, feet to cm and miles to km, and the calibrated online ruler shows both scales side by side.