Length Converter
Convert length between miles, kilometers, feet, meters, inches, centimeters, and nautical miles.
The mile-to-kilometer conversion is one I've memorized (multiply miles by 1.609 or divide kilometers by 1.609) but everything else I look up. The inch-to-centimeter conversion matters constantly for international product specs and woodworking plans that cross measurement systems.
The meter is defined exactly: 1 inch = 2.54 cm exactly by international definition (since 1959). All US customary length units are defined in terms of this exact conversion.
The metric system and SI units
The meter is the SI base unit of length, defined since 2019 as the distance light travels in a vacuum in 1/299,792,458 of a second. This definition ties the meter to a physical constant rather than a physical artifact, making it perfectly reproducible anywhere. All other metric length units are powers of ten of the meter: kilometer (1,000 m), centimeter (0.01 m), millimeter (0.001 m), micrometer (0.000001 m).
US customary length units
The US customary system uses inches, feet, yards, and miles. One foot is 12 inches. One yard is 3 feet (36 inches). One mile is 5,280 feet (1,760 yards). These conversions are historically derived from body measurements and practical standards, a foot was literally the length of a human foot, standardized over centuries of trade and law.
Nautical miles and knots
A nautical mile is 1,852 meters exactly, defined as the distance corresponding to one minute of arc along a meridian. It's used in aviation and maritime navigation because one nautical mile corresponds directly to one minute of latitude, making chart navigation mathematically convenient. A knot is one nautical mile per hour, the standard unit of speed in maritime and aviation contexts.
Frequently asked questions
How many feet are in a mile?
Exactly 5,280 feet. This oddly specific number comes from historical standardization: a mile was defined as 8 furlongs, a furlong was 40 rods, and a rod was 16.5 feet, producing 8 × 40 × 16.5 = 5,280.
Is a nautical mile longer than a regular mile?
Yes. One nautical mile is 1,852 meters (6,076 feet), compared to a statute mile of 1,609 meters (5,280 feet). A nautical mile is about 15% longer than a land mile.
What's the difference between a meter and a yard?
A yard is 0.9144 meters, about 9 cm shorter than a meter. They're close enough that rough comparisons work, but precise measurements need the actual conversion.