The perimeter of a shape is the total distance around it, while area describes the amount of surface the shape uses or covers. Perimeter and area calculation methods differ for every kind of shape. For instance, while you can find the area of a rectangle simply by multiplying its length by its width, a circle requires a more complex calculation. Learn to convert the most basic shapes' perimeters to areas and you can later progress to compound shapes.

## Squares

Divide the perimeter by four to obtain the length of each side, since all four sides of a square are equal. A square with a perimeter of 36 inches would have sides that measure 9 inches each.

Square the length of one side. For a square with 9-inch sides, the equation would be 9 x 9.

Add the proper unit of measure to the area. A square with a perimeter of 36 inches would have an area of 81 square inches.

## Rectangles

Determine the length of both the base and the height. These will be the sides that are not parallel to one another.

Multiply the base by the height.

Add the proper unit of measure.

## Triangles

Determine the length of the base of the triangle.

Calculate the height of the triangle.

Multiply the length of the base by the length of the height.

Divide by two.

Add the proper unit of measure.

## Circles

Divide the circle's perimeter, also known as circumference, by pi (3.14159265). This gives you the diameter of the circle.

Divide the diameter by two to give you the length of the radius.

Multiply the radius by itself. A 4-inch radius would multiply to 16 inches.

Multiply by pi (3.14159265).

Add the proper unit of measure.