länge

Länge is the German noun meaning length, defined as the extent of something along its longest dimension, or the distance from one point to another along a line. In German and many scientific contexts, Länge denotes what English speakers call length. The term is used in geometry, physics, engineering, and everyday measurement.

In the International System of Units (SI), the base unit for length is the meter. The meter definition has evolved: originally tied to the Earth’s meridian; since 1983 it is defined as the distance light travels in vacuum in 1/299,792,458 of a second. Other common units include the centimeter, millimeter, and kilometer, with non-SI units such as inch, foot, and mile still widely used in everyday life.

Length measurement uses rulers, tape measures, calipers, micrometers, and distance-measuring devices such as laser rangefinders or lidar. Precision and accuracy are assessed with uncertainty, instrument calibration, and standard measurement conditions.

In mathematics, length is a scalar quantity representing magnitude. In one-dimensional spaces, it equals the distance between endpoints; for curves, length is called arc length and is computed by integrating the speed along the curve; in n-dimensional Euclidean space, the length of a straight segment between points is the Euclidean distance: the square root of the sum of squared coordinate differences.

Etymology: the word Länge is native to German; the concept appears across cultures with various units and standards. See also: distance, arc length, meter, measurement.