When buying or selling a home, one big question always comes up: How does the appraisal calculate square footage?
It’s not as simple as pulling numbers from public records or a real estate listing. Instead, real estate appraisers follow strict standards, like the ANSI Z765 guidelines, to make sure the measurement is fair and accurate. That number—called gross living area (GLA)—directly affects your home’s market value and even your mortgage approval.
The Basics of Square Footage in Home Appraisals
Square footage is the backbone of a home’s value. Appraisers don’t count everything under a roof. They focus on finished, livable, heated space.
- Gross Living Area (GLA): The total above-grade finished square footage.
- Exclusions: Garages, unfinished basements, attics, porches, and decks.
- Sunrooms: Count only if enclosed, heated, and finished to standard.
I once looked at a home that was listed at 2,000 sq. ft. The appraisal knocked it down to 1,850 sq. ft. Why? The lower level wasn’t finished to ANSI standards. That 150 sq. ft. difference shaved thousands off the value.
How Appraisers Follow ANSI Standards
Most states now require appraisers to follow the American National Standards Institute (ANSI), specifically ANSI Z765-2021 for single-family homes. This standard ensures consistency.
Here’s how appraisers do it:
- Exterior wall measurements: Taken from the outside, including wall thickness.
- Tools used: Laser measurers, tape, and sometimes digital sketch software.
- Minimum ceiling height: 7 feet (or 5 feet in sloped attic spaces).
- Stairs and hallways: Count if they connect heated, finished areas.
- Basements: Always reported separately as below-grade space.
Appraisers then create a floor plan sketch—either by hand or digitally—to add up square footage for each floor.
Gross Living Area (GLA) vs. Total Living Area (TLA)
This is where most confusion happens.
- GLA: Heated, finished, above-grade, directly connected to the rest of the home.
- TLA: Includes GLA plus below-grade finished areas like basements.
Why does this matter? Lenders and underwriters (think Fannie Mae, Freddie Mac, or HUD) rely on GLA when approving loans. Overstating it in a listing can create problems during mortgage underwriting.
Why Listing Square Footage Often Differs From Appraisals
If your appraisal doesn’t match your MLS listing, don’t panic—it happens often.
Here’s why:
- Outdated tax records (from your County Assessor or Central Appraisal District).
- Unpermitted additions are not counted in official records.
- Non-livable spaces included in agent estimates (garages, porches).
- Different measurement methods (interior vs. exterior).
The Role of Heated Square Footage in Value
Not all square footage adds equal value. Appraisers give more weight to heated square footage, since it’s usable year-round.
- Above-grade finished space: Highest value per sq. ft.
- Finished basements: Add value, but at a lower rate.
- Outdoor amenities (pools, decks): Increase appeal, but not part of GLA.
Tips for Homeowners: Verify Before the Appraisal
Want to avoid surprises? You can check your own square footage before the appraiser shows up.
- Sketch each floor layout.
- Measure exterior walls with a tape measure or laser tool.
- Add up heated, finished areas only.
- Exclude garages, unfinished attics, and low-ceiling spaces.
- Update your tax assessor’s records if you’ve added finished space.
You can even hire a measurement service or an independent appraiser for peace of mind.
Final Thoughts
Understanding how the appraisal calculates square footage can save you stress during a real estate transaction. Appraisers don’t just take the seller’s word for it—they follow ANSI standards, measure carefully, and focus on gross living area.
So, if your listing square footage doesn’t match the appraisal report, it’s usually about different rules, not a mistake. Knowing this ahead of time can help you negotiate better and move through the home-buying process with confidence.
FAQs
GSF stands for Gross Square Footage. To find it, you multiply the length of a building by its width. You include all levels of the building. You also include the space taken up by walls.
To calculate the size of a survey area, you use the survey map. You find the length and width of the land. Then you multiply these numbers to get the square footage.
Square footage is found by multiplying length by width. For a room, you measure each side. Then you multiply those two numbers. This gives you the area of the room in square feet.
An appraisal is not a simple math problem. Appraisers look at many things. They look at the home’s size and condition. They also compare the home to similar homes sold nearby.
Appraisers compare square footage by looking at homes with similar sizes. They use a price per square foot. They adjust the price for differences in the homes. For example, a larger home will cost more.
To find the square footage of land, you multiply the length by the width. This works for a square or rectangle. For other shapes, you may need a land survey.
A land survey map will have numbers for each side. You use these numbers to find the area. For a rectangle, you multiply length by width. A survey for a complex shape will have the square footage on it.
The formula for area is often A = L x W. This is for a square or rectangle. For a more complex area, a surveyor uses advanced math. They may use special tools to measure the land.
Yes, you can get a rough estimate of square footage on Google Maps. There is a “measure distance” tool. You can trace an area to get a size. This is not as accurate as a real survey.
A common mistake is not measuring the right things. People often forget to include walls. Another mistake is not measuring the outside of the building. This is needed for GSF.
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