Whether you’re buying paint, carpeting, or any other type of material, knowing the square footage of the area you need to cover will help you determine exactly how much you need to purchase. Calculating square footage does require a little bit of math, but with a calculator in hand you can quickly become an old pro at calculating the space in your home. Just keep in mind that square footage describes the entire coverage area; one square foot is a square, one foot long and one foot high.
Things You'll Need
 Tape measure that measures in inches
 Calculator
Calculate Square Footage of a Rectangle

Measure the length of the area with your tape measure. Record the result in inches.

Measure the width of the area with your tape measure. Record the results in inches.

Multiply the inches in Step 1 by the inches in Step 2. This gives you the area's size in square inches.

Convert the square inches into square feet by dividing the number of square inches by 144 (because a square foot is 12 inches by 12 inches). This is your room's area in square feet.
Calculate Square Footage of a Circular Area

Measure the distance from one side of the circle to the other (the diameter) in inches.

Divide the diameter of the circle by 2. This is the circle's radius.

Multiply the following:
Radius x Radius x 3.14
The answer is the circle's size in square inches.

Divide the result from Step 3 by 144 to arrive at the area's square footage.
 Photo Credit tape measure image by Alison Bowden from Fotolia.com