of length is a base unit, from which other units are derived. Contents History edit Measurement has been important ever since humans settled from nomadic lifestyles and started using building materials, occupying land and trading with neighbours. Historically, units of length may have been derived from the lengths of human body parts, the distance travelled in a number of paces, the distance between landmarks or places on the Earth, or arbitrarily on the length of some fixed object. Thus a ruler that is one meter long in one frame of reference will not be one meter long in a reference frame that is travelling at a velocity relative to the first frame.

In other contexts, length is a measured dimension of an object. See also edit References edit). In the International System of Units (SI the basic unit of length is the metre and is now defined in terms of the speed of light. Length is a measure of one dimension, whereas area is a measure of two dimensions ( length squared) and volume is a measure of three dimensions ( length cubed). 1, in the, international System of Quantities, length is any quantity with dimension distance. Units used to denote distances in the vastness of space, as in astronomy, are much longer than those typically used on Earth and include the astronomical unit, the light-year, and the parsec.