ANSI Z765: The Standard for Measuring Square Footage
ANSI Z765-2021 is the national standard for measuring and reporting a single-family home's square footage. It's voluntary, but Fannie Mae has required it for appraisals since April 1, 2022 and Freddie Mac since November 2, 2023. Its core rules: measure the outside of the exterior walls, count only finished above-grade space with a 7 foot ceiling, and report below-grade area separately.
- Is it required?
- Homes covered
- Core rules
- Ceiling height
- Basements
- Stairs
- Why ANSI numbers differ
- What it doesn't cover
- FAQ
Is ANSI Z765 required?
No law requires it. Home Innovation Research Labs describes ANSI Z765 as a voluntary standard; the mortgage buyers are what make it mandatory.
Appraisals with interior and exterior inspections (Appraisal Institute), now also hybrid appraisals. Desktop appraisals are exempt (Fannie Mae).
Properties that need an interior and exterior inspection (Pennsylvania Association of Realtors).
These programs allow ANSI measurement but don't require it, per the same Realtors' summary.
If a state requires another method, the appraiser must say so and explain how it was applied (Fannie Mae).
The GXX001 exception code is retired. Fannie Mae now requires full compliance with no opt-out. Appraisers explain limits, such as measuring from plans, with ANSI declarations instead.
Which homes it covers
ANSI Z765 covers single-family houses, detached or attached, whatever the ownership type.
Detached houses, townhouses, rowhouses, manufactured homes and accessory dwelling units, including condos built as townhouses.
Units in apartment-style or multifamily buildings, which Fannie Mae measures by interior perimeter. ANSI generally isn't required for outbuildings (Fannie Mae).
The core measurement rules
Six rules turn a house into an ANSI number. What each one includes is listed room by room in what counts as square footage.
- Measure the outside of the exterior walls to the nearest inch or tenth of a foot. That's why an ANSI figure comes out larger than a room-by-room total: on a house the size of the median new home, 2x6 exterior walls alone add about 99 to 139 square feet, and gross vs net square footage sizes the gap for any house.
- Count only finished living area: finished, heated and directly reachable from the rest of the house. Garages and unfinished space stay out. Even an attached garage stays out unless it has been converted; see when a garage counts as square footage.
- Report above-grade and below-grade area separately.
- Apply the 7 foot ceiling rule to every finished room.
- Count stairs on the floor they descend from and leave out openings to the floor below.
- Round the final total to the nearest whole square foot. Fannie Mae also requires a computer-generated sketch.
The total of finished above-grade space is the home's gross living area. ANSI doesn't change the geometry; how to calculate square footage covers the length times width math. For a rough check of your own, the square footage calculator will add up several rooms into one total, but applying the six rules above is up to you.
The ceiling-height rule
Finished area needs a 7 ft ceiling. Under a slope, at least 50% of the room must be 7 ft or taller, and no part under 5 ft counts.
Most homes clear that minimum easily; see standard ceiling heights by era and floor.
A room that fails isn't erased. Fannie Mae has it reported as nonstandard finished area, a separate line the appraiser still values by market reaction. The worked cases are in does a finished attic count as square footage.
Basements and below-grade space
A level with any part of its walls below ground is reported as below-grade area, however well it's finished. That includes a finished walkout basement with a door at ground level.
The basement still adds value; it's just listed on its own line. See above-grade vs below-grade square footage and does a basement count as square footage.
Stairs and open areas
A staircase counts once, on the floor it descends from, and open space over a lower floor never counts.
A flight from the first to the second floor counts in the second floor's area.
Openings to the floor below, such as two-story foyers, aren't included (Fannie Mae).
Where the opening is wider than the stairs, the extra width is deducted (NCREC).
Numbers for each case are in do stairs count as square footage.
Why ANSI numbers differ from MLS and tax records
Those figures often weren't measured under ANSI. Fannie Mae says MLS and assessor square footage "may not have been derived using the ANSI standard," so a smaller appraisal is usually the stricter rule at work, not an error.
How square footage is measured in real estate explains who produces each number. To check a house yourself, total the finished above-grade rooms in the house square footage calculator and keep the basement separate.
What ANSI Z765 doesn't cover
ANSI Z765 sets how area is measured and reported, nothing more.
Home Innovation says the standard does not cover room dimensions, so it has no bedroom rules.
Fannie Mae: adherence to the standard does not change the value of the property.
Offices, stores and apartment buildings use other measures, such as gross floor area; see commercial square footage.
Frequently asked questions
What are the national requirements for measuring a dwelling's square footage?
There's no federal law. The national standard is ANSI Z765-2021, which Fannie Mae and Freddie Mac require for most appraisals on the loans they buy.
What does ANSI Z765 stand for?
ANSI is the American National Standards Institute. Z765 is the standard's number, and its title is Square Footage: Method for Calculating. The current edition is 2021.
What is the ANSI ceiling height requirement?
Finished area needs a ceiling of at least 7 feet. In a sloped room, at least half the floor must have 7 feet of headroom, and any part under 5 feet is left out.
What replaced the GXX001 exception code?
Nothing. Fannie Mae retired GXX001 and requires full ANSI compliance. Appraisers use ANSI declarations to explain limits, or cite the state law that requires a different method.
Where can I get the ANSI Z765-2021 PDF?
It isn't free. Home Innovation Research Labs sells the PDF for $25 on its store page, and Fannie Mae's free ANSI FAQ summarizes the main rules.
Does a finished basement count under ANSI Z765?
Not in gross living area. Any level with part of its walls below ground is reported as below-grade finished area on a separate line.