The Foolproof Way to Calculate Your Home’s Square Footage

updated Aug 11, 2023
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woman measuring wall with measuring tape
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If you’re in the market for a new home or it’s time to list your own, you’ve probably come across the term “square footage.” Ahead, find the best way to measure the square footage of your home. 

What is square footage?

Square footage is the measurement of the total area of a space. Many areas of the home are measured in square feet, including the rooms, garage, porches, and patios. To calculate square footage, think back to high school geometry — the area of a square is equal to its length multiplied by its width.

The total square footage of a home is what’s known as the gross living area, or GLA, which equals the square footage of all living areas in the home added together. The GLA is related to the home’s price, but there are a lot of factors in a home appraisal that determine a home’s price per square foot. And just looking at this number leaves a lot to the imagination.

Factors that influence a home’s price per square foot include:

  • Interior finishes
  • Amenities such as a pool, deck or porch, garage, wine cellar, sauna, etc.
  • Updates to the bedrooms, kitchen, bathroom, etc.

The American National Standards Institute (ANSI) lays out rules for calculating square footage, which have been adopted by Fannie Mae and must be used when appraisers are calculating square footage for a Fannie Mae loan. While you can calculate square footage from the interior of the home, appraisers actually measure from the exterior and then analyze the interior to come up with the final calculation.

Credit: Design: Apartment Therapy

How to Calculate Square Footage

There are two methods for calculating square footage, but to get the most accurate measurements, you should use both and compare.

Method 1: Measure the Exterior

To measure the exterior of the home, sketch the home’s footprint and then measure the length of each wall in feet. Appraisers using the ANSI standards must use a computer generated sketch of the home. 

Once each wall is labeled, break the space down into rectangles and then multiply the length and the width. If there are other shapes to consider, you can use a square footage calculator to help. Add up all the totals to come up with the final calculation.

Credit: Naruedom Yaempongsa/

Method 2: Measure the Interior

To determine the square footage using this method, take the measurement of each room by measuring the length and the width in feet and then multiplying the numbers together.

For irregularly shaped rooms, you can use a square footage calculator. You can also split the room into smaller squares, measuring and calculating the square footage of each and then adding them together for the total. 

If a room is triangular, the bottom of the triangle is the “base” and the distance from the base to the tip is the “height.” Multiply the base times the height and divide by 2 to get the area. For a circular (or semi-circular) shaped room, measure from the center to the edge to find the radius, and then multiply that number by pi (3.14). If it’s a semicircle, divide that number by two.

Add up all of the totals to come up with the final calculation. Be sure to measure all finished spaces that are heated and cooled, including closets. When accounting for staircases, count them toward the square footage of the floor from which they descend. 

The total of the exterior calculation won’t match the interior calculation exactly because it includes the exterior and interior walls, but it will allow you to subtract any space that doesn’t count toward GLA.

What Doesn’t Count Towards GLA

  • Unfinished areas including the garage and attic
  • Finished areas with a ceiling height less than 7 feet for 50 percent or more of the area
  • Finished areas with a ceiling height less than 5 feet
  • Accessory dwelling units including pool houses, guest houses, and sheds
  • Areas that are heated and cooled differently from the rest of the home — or not heated and cooled at all 
  • Two story foyers only count toward the square footage on one floor
Credit: dnd_project/Shutterstock

The Foolproof Way to Calculate Square Footage — The Bottom Line

To accurately calculate square footage, the best method is to hire a licensed appraiser. It will probably cost less than $200, and you’ll be assured that they’re using their professional knowledge and experience to get the most accurate measurement. 

You can also measure the home yourself using the same method they use. If you feel like there’s a discrepancy between their number and your number, you can discuss any inconsistencies to make sure you have the most accurate calculation. If you’re looking for an extra hand, your real estate agent can also help you measure.