Metric Units

Meter (m): The SI base unit of length, defined as the distance traveled by light in vacuum in 1/299,792,458 of a second.

Kilometer (km): 1,000 meters, used for longer distances like city-to-city travel.

Centimeter (cm): 0.01 meters, used for everyday small measurements.

Millimeter (mm): 0.001 meters, used in precision engineering and manufacturing.

Micrometer (μm): 0.000001 meters, used in microbiology and semiconductor manufacturing.

Nanometer (nm): 0.000000001 meters, used in nanotechnology and molecular studies.

Imperial/US Units

Inch (in): 0.0254 meters, the smallest common unit in the Imperial system.

Foot (ft): 12 inches or 0.3048 meters.

Yard (yd): 3 feet or 0.9144 meters.

Mile (mi): 5,280 feet or 1,609.344 meters.

Mil (thou): 0.001 inches or 0.0000254 meters, used in engineering.

Maritime and Navigation Units

Nautical Mile (nmi): 1,852 meters, defined as one minute of latitude.

Fathom: 6 feet or 1.8288 meters, used to measure water depth.

Astronomical Units

Astronomical Unit (AU): The average distance from Earth to the Sun (about 149.6 million kilometers).

Light Year (ly): The distance light travels in a year (about 9.461 trillion kilometers).

Parsec (pc): About 3.26 light years or 30.9 trillion kilometers.

Historical Units

Furlong: 220 yards or 201.168 meters, originally the length of a furrow in an acre-sized field.

Chain: 66 feet or 20.1168 meters, used in land survey.

League: Approximately 3 miles or 4.83 kilometers.

Conversion Factors

Key conversion factors between common distance units:

• 1 inch = 2.54 centimeters
• 1 foot = 0.3048 meters
• 1 yard = 0.9144 meters
• 1 mile = 1.60934 kilometers
• 1 nautical mile = 1.852 kilometers
• 1 light year = 9.461 × 10^15 meters