How to Calculate Square Footage

The next step in how to calculate square footage is to plug your measurements into the square footage formula: L x W = A (in square feet).

How to find square feet: multiply the length measurement in feet by the width measurement (in feet). This yields a product called the area, which is expressed in square feet (or square inches if you are calculating a much smaller space, such as a dollhouse). 

For example, if you are buying carpet for a room that is 12-feet long and 10-feet wide, multiply the two dimensions: 

• 12 ft. x 10 ft. = 120 sq. ft.

Sometimes you will have to account for odd room dimensions or additional areas that don't neatly connect with your main room. In this case, to calculate the square footage accurately, you may need to divide the space into separate areas. 

• Divide the space into smaller sections.
• Measure each section separately and calculate the square footage of each.
• Use a calculator to add the numbers together to get the total square footage.

For example, assume you are trying to buy flooring for a rectangular room with a nook. The shape is of a large rectangle and a smaller rectangle. 

• Find the length and width of each section (labeled A and B here), then calculate each square footage:

A: 3 ft. x 7 ft. = 21 sq. ft. 

B: 12 ft. x 10 ft. = 120 sq. ft.

• Then, add the three values together to get the total square footage you’ll need:

120 sq. ft. + 21 sq. ft. = 141 sq. ft.

• Therefore, you’ll need 141 sq. ft. of flooring materials.

Once you’ve found the quantity of material you need to complete your project, adjust the amount for waste. This doesn’t mean that you are planning to waste the materials, but mistakes can happen. If you accidentally break tiles or spill paint and you have only the exact amount you needed, you may find yourself scrambling to replace your materials. Or worse, in the case of some materials, you may find yourself unable to get an exact color match with the first batch you ordered. 

Order 5 to 10 percent more of your materials than you have calculated. This way, you're covered.  

Materials like tile can often be returned if they haven’t been opened or used, so that you can recover a little of your extra cost once the project is complete. However, you may find it helpful to store the extra materials, in case you need to replace tiles, patch carpet or touch up paint down the road.  

In addition to making home improvement projects easier, knowing how to calculate square footage makes you a more knowledgeable home buyer and home seller. Learn this simple skill to compare properties when purchasing. Knowing how to calculate this measurement is useful for evaluating or comparing properties when you're the seller. Knowing your property's square footage helps when you need a building permit to convert an unused basement or attic into living space.

Tip: The square footage of a house usually includes finished living spaces that includes walls, floors, ceilings and heat. This can include finished attics, basements, garages and staircases.