A quadrilateral with both pairs of opposite sides parallel and all sides the same length, i.e., an equilateral parallelogram. The word rhomb is sometimes used instead of rhombus, and a rhombus is sometimes also called a diamond. A rhombus with is sometimes called a lozenge.

The polygon diagonals and of a rhombus are perpendicular and satisfy

(1)

The diagonals are related to the opening angle by

			(2)
			(3)

The area of a rhombus is given by

			(4)
			(5)
			(6)

The rhombus is a tangential quadrilateral with , and so has inradius

(7)

Beyer, W. H. (Ed.). CRC Standard Mathematical Tables, 28th ed. Boca Raton, FL: CRC Press, p. 123, 1987.

Harris, J. W. and Stocker, H. "Rhombus." §3.6.4 in Handbook of Mathematics and Computational Science. New York: Springer-Verlag, pp. 83-84, 1998.

CITE THIS AS:

Weisstein, Eric W. "Rhombus." From MathWorld--A Wolfram Web Resource. http://mathworld.wolfram.com/Rhombus.html