Editing Length (section)

=== Euclidean geometry ===
{{main|Euclidean geometry}}
In Euclidean geometry, length is measured along [[straight line]]s unless otherwise specified and refers to [[line segment|segments]] on them. [[Pythagorean theorem|Pythagoras's theorem]] relating the length of the sides of a [[right triangle]] is one of many applications in Euclidean geometry. Length may also be measured along other types of curves and is referred to as [[arclength]].

In a [[triangle]], the length of an [[Altitude (triangle)|altitude]], a line segment drawn from a vertex [[perpendicular]] to the side not passing through the vertex (referred to as a [[Base (geometry)|base]] of the triangle), is called the height of the triangle.

The [[area]] of a [[rectangle]] is defined to be length&thinsp;×&thinsp;width of the rectangle. If a long thin rectangle is stood up on its short side then its area could also be described as its height&thinsp;×&thinsp;width.

The [[volume]] of a [[Rectangular cuboid|solid rectangular box]] (such as a [[plank of wood]]) is often described as length&thinsp;×&thinsp;height&thinsp;×&thinsp;depth.

The [[perimeter]] of a [[polygon]] is the sum of the lengths of its [[Edge (geometry)|sides]].

The [[circumference]] of a circular [[Disk (mathematics)|disk]] is the length of the [[Boundary (of a manifold)|boundary]] (a [[Circle (geometry)|circle]]) of that disk.