– Metric System:
– Base unit in SI is the meter
– Meter defined as the path light travels in vacuum in 1299792458 seconds
– SI units derived from meter with prefixes like millimeter or kilometer
– Kilometer equals 1000m
– Non-SI units in centimeter-gram-second system derived from multiples of meter
– Imperial/U.S. Units:
– Basic unit is the yard
– Yard defined as exactly 0.9144m by international treaty in 1959
– Common units include thou, inch, foot, yard, mile, and league
– Inch equals 25.4mm
– Mile equals 5280 feet or 1609.344m
– Marine Measurements:
– Used by sailors: fathom and nautical mile
– Fathom equals 2 yards or 1.8288m
– Nautical mile equals 1852m
– Aviation Measurements:
– Aviators use feet for altitude worldwide
– Nautical miles used for distance
– Exception in Russia and China
– Citation needed for further information
– Surveying Units:
– Surveyors in the U.S. use chain and rod
– Chain equals 22 yards or 20.1168m
– Rod equals quarter of a chain or 5.0292m
– Determination of the rod based on the length of the left foot of 16 people
– Surveying units used for land measurement
– Building Trades Units:
– Australian building trades use meters and millimeters
– Centimeters avoided for clarity
– Two and a half meters recorded as 2500mm or 2.5m
– Non-standard to record as 250cm
– Metric system adopted by Australian building trades in 1966
– Surveyors Trade Measurements:
– American surveyors use a decimal-based system devised by Edmund Gunter
– Base unit is Gunter’s chain of 66 feet
– Chain subdivided into 4 rods
– Each rod equals 16.5 feet or 100 links of 0.66 feet
– Links abbreviated as lk and lks in old deeds
– Science Measurements:
– Astronomical measurements include Earth radius and lunar distance
– Astronomical unit defined as 149597870700m
– Light-year equals about 9460730472580.8km
– Parsec approximately 3.26156 light-years
– Quantum chromodynamics unit of length and natural units based on the electronvolt
This article needs additional citations for verification. (October 2012) |
A unit of length refers to any arbitrarily chosen and accepted reference standard for measurement of length. The most common units in modern use are the metric units, used in every country globally. In the United States the U.S. customary units are also in use. British Imperial units are still used for some purposes in the United Kingdom and some other countries. The metric system is sub-divided into SI and non-SI units.
