Length or distance is a measurement of the extent of something from end to end or the amount of space between two things or people. It’s a fundamental dimension in most physical systems and is used to define spatial (3D) quantities. Here are the commonly used units for length/distance:
Metric System (International System of Units, SI):
- Millimeter (mm): One thousandth of a meter.
- Centimeter (cm): One hundredth of a meter.
- Meter (m): The basic unit of length in the metric system.
- Kilometer (km): One thousand meters.
Imperial (or US Customary) System:
- Inch (in): 1/12th of a foot.
- Foot (ft): Contains 12 inches.
- Yard (yd): 3 feet or 36 inches.
- Mile (mi): 5,280 feet or 1,760 yards.
Nautical:
- Nautical Mile: Used in marine navigation, it’s equal to one minute of latitude. It’s approximately 1.852 kilometers or 1.15078 statute miles.
Astronomical:
- Astronomical Unit (AU): Average distance from Earth to the Sun, approximately 93 million miles (150 million kilometers).
- Light Year: The distance that light travels in one year, roughly 9.461 trillion kilometers or 5.879 trillion miles.
- Parsec: Equal to about 3.26 light years.
The choice of unit is often determined by the context. For example, when measuring the width of a human hair, millimeters or micrometers might be more appropriate. But when measuring the distance between cities, kilometers or miles would be more suitable. In science and engineering, the metric system is widely adopted because of its ease of use and universal standardization.