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

## Area of a Circle

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

**Area = pi (r x r)**

## Area of a Ellipse

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

**Area = pi (r1 x r2)**

## Area of a Triangle

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

**Area = (h x B)/2**

## Area of a 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**

## Area of a 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**

## Area of a 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**

## Area of a 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))**

## Area of a Quadrilateral

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