How to Calculate a Home’s Square Footage

Not everyone in the real estate business calculates square footage the same way. In fact, it may be different from one geographic area to the next. The square footage listed in the county records for condominium units is typically not questioned. These numbers are taken from the original condominium documents and are generally accurate. Unlike detached homes, square footage is less likely to change on a condominium as a result of additions and improvements.

For attached and detached single-family homes, there are different ways to calculate square footage. Most real estate appraisers measure the exterior of the home to calculate the gross living area. For example, a two-story home that measures 30 feet by 45 feet would have 1,350 square feet on each floor, so the appraiser would say the house contains 2,700 square feet. Since he is measuring from the exterior, the calculation includes hallways, stairwells, closets, and wall space.

The basement is another consideration even though we don’t have many in the San Antonio area. The appraiser would determine how much of the basement has been finished as living area. Instead of totaling the square footage of a basement’s living area, he will make value adjustments based on other comparable homes. For example, a home with a full finished basement that includes a family room, bathroom and bedroom might be credited $15,000 or $20,000 in value compared to a similar house with an unfinished basement. In some cases, even if the lowest level is completely above grade, an appraiser may treat it as a basement. Consider an attached townhouse that has a lower level used as a garage and a family room. An appraiser might treat such a room as a basement.

It gets more complicated. What if the house in our example has a vaulted ceiling in the family room with a second story balcony? This would clearly result in the second floor having less than 1,350 square feet of actual floor area. Most appraisers won’t subtract the space left out of the second floor to make room for the vaulted ceilings. Why? Because such a floor plan often enhances the market value of the home because it’s a popular feature to have. Remember that an appraiser’s job is to determine the market value of the home. The total size of the living area is only part of the equation.

Many real estate agents and builders will include all finished “walkable” areas when totaling the square feet of a house. It’s certainly not misleading. A lot of prospective homebuyers would want to know the total living area, regardless of whether some of it is below grade.

Other real estate agents will use the square footage that’s listed in the county tax records in their marketing materials. Unfortunately, this information is often incorrect, especially with older homes. Over time additions are constructed, increasing the chances that tax records will be outdated and inaccurate. It’s for this reason that some agents simply choose to calculate the square footage in the listing. You’ve probably seen a disclaimer similar to this on an MLS listing: “All measurements, taxes, age, financial & school data are approximate and provided by other sources.  Buyer should independently verify the same before relying thereon.” 

The bottom line? Calculating the square footage of a home is more of opinion than an exact science. If you’re interested in buying a particular house and want to know the size expressed in square feet, my advice would be to make an appointment to visit the home and bring your tape measure, pen, paper, and calculator.