| non-negative additive quantity attributed to a one-dimensional object in space|
NOTE 1 Length is one of the base quantities in the International System of Quantities (ISQ) on which the International System of Units (SI) is based.
NOTE 2 The length of a curve and the distance of two points are defined in IEC 60050-102:2007 (102-04-18 and 102-03-24).
NOTE 3 The term length is also used by convention for the greatest dimension of an object, as distinguished from breadth and from height or thickness.
NOTE 4 The coherent SI unit of length is metre, m (see IEC 60050-112:2010, 112-02-05). Non-SI units used by special interest groups are ångström, Ǻ (1 Ǻ:= 10−10 m), and nautical mile (1 nautical mile:= 1 852 m). A unit accepted in use with the SI, whose value must be obtained experimentally, is astronomical unit, ua, approximately equal to the mean Earth-Sun distance.