Finding Area

Updated May 8, 2019 | Infoplease Staff

Square

A = a², in which a is one of the sides.

Rectangle

A = ab, in which a is the base and b is the length.

Parallelogram

A = bh, in which b is the base and h is the height.

Circle

A = πr², in which π is 3.1416 and r is the radius.

Ellipse

A = πr₁r₂, in which π is 3.1416, r₁ is the longer radius, and r₂ is the shorter radius.

Trapezoid

A = (h[b₁ + b₂])/2, in which h is the height, b₁ is the longer parallel side, and b₂ is the shorter parallel side.

Triangle

Given base and height: A = (1/2)bh, in which b is the base and h is the height.

Given side, angle, side (SAS): (1/2) ab x sinθ, in which a is one side, b is another side, and θ is the known angle.

Given three sides: when s = (a + b + c)/2 (Heron's formula), in which a, b, and c represent the three sides.