Length conversion covers 19 units. Below is a plain-English definition of each one and where you'll actually meet it in daily life.
Meter (m)
The meter is the SI base unit of length, defined by the distance light travels in a vacuum in 1/299,792,458 of a second.
Used for: Used for room dimensions, sports track distances, fabric and construction measurements across most of the world.
Kilometer (km)
A kilometer is 1,000 meters, the standard unit for long distances in the metric system.
Used for: Road signs, running races (5K, 10K, marathon), and geographic distances in metric countries.
Centimeter (cm)
A centimeter is one-hundredth of a meter, roughly the width of a fingernail.
Used for: Clothing sizes, screen and paper dimensions, rainfall measurements, and everyday object sizes.
Millimeter (mm)
A millimeter is one-thousandth of a meter, about the thickness of a credit card.
Used for: Engineering drawings, machining tolerances, 3D-printing layer heights, and precipitation records.
Micrometer (µm)
A micrometer (micron) is one-millionth of a meter, roughly the size of a bacterium.
Used for: Precision manufacturing tolerances, coatings and film thickness, and semiconductor feature sizes.
Nanometer (nm)
A nanometer is one-billionth of a meter, about the width of a few atoms.
Used for: Wavelengths of visible light (400–700 nm) and the critical dimensions of computer chips.
Mile (mi)
A mile is 5,280 feet or exactly 1,609.344 meters, the standard long-distance unit in the US and UK.
Used for: Driving distances, speed limits, and running races such as the 5-mile and half-marathon in imperial countries.
Yard (yd)
A yard is 3 feet or 0.9144 meters.
Used for: American football field lengths, fabric sales, and golf course distances in the US and UK.
Foot (ft)
A foot is 12 inches or exactly 0.3048 meters.
Used for: Human height, aviation altitudes, room dimensions, and construction lumber in the US and UK.
Inch (in)
An inch is 1/12 of a foot, exactly 25.4 millimeters.
Used for: Screen diagonals, paper sizes, pipe and tire diameters, and fastener sizes in imperial countries.
Nautical Mile (nmi)
A nautical mile is exactly 1,852 meters, defined as one minute of latitude.
Used for: Aviation and maritime navigation, where one nautical mile per hour equals one knot.
Decimeter (dm)
A decimeter is one-tenth of a meter, about the width of an adult hand.
Used for: Hydrology (river depths), aquarium dimensions, and some scientific volume calculations.
Gaj (gaj)
A gaj (or square gaj in area contexts) equals one yard, 0.9144 meters.
Used for: Indian real-estate listings, where land and room sizes are commonly quoted in gaj.
Hath (Cubit) (hath)
A hath is a traditional South Asian unit of length equal to 2 feet (0.4572 meters).
Used for: Traditional markets in India and Bangladesh for cloth and construction materials.
Kosh (kosh)
A kosh is a traditional Indian distance unit historically set at about 3 kilometers (3,000 meters).
Used for: Historic road distances in India; still referenced in older land records and folklore.
Furlong (fur)
A furlong is 220 yards or exactly 201.168 meters.
Used for: Horse racing distances, and historic farmland measurements that survive in UK and US records.
Chain (ch)
A chain is 66 feet or exactly 20.1168 meters, made of 100 links.
Used for: Surveying; cricket pitch length is one chain (22 yards).
Link (li)
A link is 1/100 of a surveyor's chain, exactly 0.201168 meters.
Used for: Land surveying subdivisions, mostly in historical US public-land records.
Rod (rd)
A rod (or perch) is 16.5 feet or exactly 5.0292 meters.
Used for: Historic land area measurements; still used for some fishing and fencing specifications.