If you buy or sell a home, one of the most important parts of the real estate appraisal process is figuring out the square footage. This number isn’t just pulled from tax records or MLS listings. Instead, appraisers follow strict standards to measure the gross living area (GLA). That number directly affects your home’s market value and the outcome of your sale or mortgage.
Let’s break down how appraisers calculate square footage. What standards they follow (like ANSI Z765), and why your listing square footage may not match your appraisal.
The Basics of Square Footage in Home Appraisals
In real estate, square footage is more than a number—it’s the foundation for how property value is estimated.
Appraisers focus on finished, livable, heated space that meets housing standards. They don’t just take the home’s outside dimensions and call it a day.
- Gross Living Area (GLA): Above-ground, finished, and heated space under the main roof.
- Excluded spaces: Garages, unfinished basements, attics, porches, and carports.
- Condition matters: A sunroom only counts if it’s enclosed, climate-controlled, and finished to match the home.
Public records, such as those from the county tax assessor or Central Appraisal District (CAD), may provide a baseline. But these are often outdated, especially if renovations weren’t reported. That’s why appraisers perform a physical property inspection.
How Appraisers Follow ANSI Standards
To keep things consistent, most appraisers now follow the ANSI Z765 measurement standard. This standard was adopted by Fannie Mae in 2022 for single-family homes, and many lenders now require it.
Here’s how ANSI works:
- Exterior wall measurements: Taken from the outside walls, including wall thickness.
- Precision tools: Laser measurers or tape to the nearest inch.
- Rounding: Final numbers are rounded to the nearest square foot.
What Counts Toward GLA:
- Above-grade finished areas with a ceiling height of at least 7 feet (5 feet for sloped ceilings).
- Stairs and hallways that connect the livable space.
- Finished attics (only if heated and meeting height requirements).
What Doesn’t Count:
- Basements: Even finished ones are classified as below-grade and reported separately.
- Garages, porches, and decks: These are listed as amenities but excluded from GLA.
Appraisers either hand-sketch floor plans or use digital appraisal software like ACI or TOTAL. Each level is measured separately and then combined.
Gross Living Area (GLA) vs. Total Living Area (TLA)
This is where many homeowners get confused.
- GLA: Heated, finished, above-grade, directly accessible from the rest of the home.
- TLA (Total Living Area): Includes below-grade finished basements or walkouts but is reported separately.
For condos and townhomes, ANSI adjusts to interior wall measurements since exterior walls are shared.
This distinction matters because mortgage lenders like Freddie Mac and Fannie Mae rely on GLA to approve loans. Overstating square footage can create problems during underwriting.
Why Listing Square Footage Differs from the Appraisal
It’s common for MLS listings and appraisal reports to show different numbers.
Here’s why:
- Tax records: May be outdated if additions or remodels weren’t reported.
- Agent estimates: Realtors sometimes measure from interior walls or include unfinished basements.
- Ceiling heights: Some basements or attic spaces don’t meet ANSI’s 7-foot rule.
Example: A home listed as 2,000 square feet might appraise at 1,850 because a basement rec room didn’t meet ANSI’s requirements. That 150-square-foot difference could impact the home’s appraised value by thousands of dollars.
Heated Square Footage and Amenities
Not all square footage is valued the same way.
- Heated square footage = GLA: Must use a permanent system like HVAC, radiant floor heating, or mini-splits. Portable heaters don’t qualify.
- Finished quality: Drywall, flooring, and trim must meet standard residential finishes.
- Amenities: Decks, pools, and outdoor kitchens add value but aren’t counted as GLA.
Appraisers note them separately and adjust value by comparing similar homes with those features.
Tips for Verifying Your Home’s Square Footage
Before your appraisal, it helps to double-check your own numbers.
Here’s how:
- Sketch each floor.
- Measure outside dimensions with a tape or laser.
- Multiply length × width for each finished, heated space.
- Exclude garages, unfinished basements, and areas with less than 5-foot ceilings.
- Add the total for each level.
If you’ve renovated, update your county assessor records to reflect changes. You can also hire a professional property measurement service for accuracy.
Final Thoughts
Square footage is the backbone of real estate appraisals. By following ANSI Z765, appraisers ensure consistency, accuracy, and fairness in determining value.
- GLA = above-grade, finished, heated space
- Basements = reported separately
- Discrepancies = normal but explainable
If your appraisal comes back with lower square footage than your listing, don’t panic. Review the report, check your records, and if needed, provide documentation such as blueprints or building permits.
At the end of the day, accurate square footage helps buyers, sellers, lenders, and appraisers all stay on the same page—leading to smoother transactions and fair market value.
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.
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.
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.
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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