Area

Below are a series of diagrams that demonstrate how to calculate the area of two dimensional shapes.

Circle

The area of a circle is the product of pi and the square of the radius.

Area = pi (r x r)

Ellipse

An ellipse is flattened circle so the area calculation takes into account that there are two different radii.

Area = pi (r1 x r2)

Triangle

The area of a triangle is half of the product of the base and height.

Area = (h x B)/2

Equilateral Triangle

An equilateral triangle has 3 equal length sides.  While the formula above will also work, there is an alternative method of calculating the area of an equilateral triangle.

Area = ((sqrt 3) (A x A)) / 4

Rectangle

The area of a rectangle is the product of the long side and the short side.  The area of a square is the length of a side squared.

Area = A x B 

Parallelogram

A parallelogram is rectangle that is skewed slightly.  The area is a product of the base and the overall height.

Area = B x h 

Trapezoid

Trapezoids are half of a parallelogram.  The diagram at left shows how 2 equal trapezoids make a parallelogram.  Therefore, the area calculation is simply half of the area of a parallelogram.

Area = 1/2 (h (A + B))

Quadrilateral

A quadrilateral is simply two triangles put together, so the area can be calculated by summing the areas of the two triangles.