"How many square feet is this house?" sounds like a simple question, but the answer depends entirely on which spaces you count. A finished bedroom clearly counts. A detached garage clearly does not. In between sits a long list of gray areas — basements, attics, sunrooms, porches — where buyers, sellers, appraisers, and tax assessors often disagree. Getting it wrong can misprice a home by tens of thousands of dollars.
This guide explains the industry rules for gross living area (GLA), the figure most appraisals and listings rely on. You will learn the three tests a space must pass to count, why garages and unfinished basements are excluded even when they are attached to the house, how finished basements are reported separately, and why the number on your tax card rarely matches the appraisal. If you want to run the figures yourself, our whole house calculator adds it all up.
The three tests a space must pass
Under the ANSI Z765 standard that most appraisers follow, a space only counts toward gross living area if it is finished, heated, and above grade. "Finished" means it has the same wall, floor, and ceiling materials you would expect in the rest of the living area. "Heated" means it is served by the home's conventional, permanent heating system. "Above grade" means the floor sits at or above ground level on all sides.
Miss any one of these and the space drops out of the main square-footage figure. A beautifully finished, carpeted room with no heat source does not count. A heated, finished room whose floor sits below ground level does not count as above-grade living area — though, as you will see below, it may be reported separately. These three tests are the backbone of every rule that follows.
- Finished: standard interior wall, floor, and ceiling finishes throughout.
- Heated: connected to the home's permanent, conventional heating system.
- Above grade: the floor is at or above ground level on every side.
- Accessible: reachable directly from other living areas, not only through a garage or by a ladder.
Why garages never count
A garage does not count toward living area, and this surprises a lot of homeowners because an attached garage shares a wall with the house. But a standard garage is unfinished and unconditioned — bare framing or drywall, an uninsulated slab, and no permanent heat. It fails the "finished" and "heated" tests immediately, so whether it is attached, detached, or tucked under the house makes no difference to GLA.
The exception is a full, permitted garage conversion. If the space has been properly finished, insulated, heated by the home's system, and its floor is at grade, it can be counted like any other room — but only when the conversion is genuine and, ideally, permitted. A half-finished garage with a space heater still counts as a garage. If you are weighing a conversion, our does a garage count calculator shows the potential added area.
Basements: finished, but reported separately
Basements are the single biggest source of square-footage confusion. An unfinished basement — concrete floor, exposed joists, storage and utilities — does not count toward anything. A finished basement is different: it can be excellent living space, but because its floor sits below grade, it is not added to your above-grade GLA. Instead, standards call for it to be reported separately as finished below-grade area.
That is why a listing might read "1,800 sq ft plus a 900 sq ft finished basement" rather than simply "2,700 sq ft." The distinction protects buyers: below-grade space typically appraises at a lower value per square foot than above-grade living area, so lumping the two together overstates the home. Even a walkout basement, finished to the same standard as the upstairs, is kept in its own line. Use our finished basement calculator to size that space on its own.
Attics, bonus rooms, and the 7-foot ceiling rule
A finished attic or bonus room can count toward GLA, but sloped ceilings add a wrinkle. The ANSI rule is specific: at least half of the room's finished floor area must have a ceiling height of at least 7 feet. If the space clears that bar, you count the floor area where the ceiling is at least 5 feet tall. Floor space under a ceiling lower than 5 feet is excluded entirely.
So a converted attic that is 20 feet by 15 feet on the floor might contribute far less than 300 square feet once the low knee-wall edges are trimmed off. The room also has to be finished, heated, and reachable by a conventional staircase — an attic you enter by pull-down ladder does not qualify. Our attic calculator handles the ceiling-height math for you.
The spaces that don't make the cut
Beyond garages and unfinished basements, several common features are left out of living area because they fail one of the three tests. Open porches and decks are excluded because they are not enclosed living space. An unheated, three-season sunroom is excluded even though it is finished, because it lacks permanent heat. Detached structures — pool houses, sheds, guest cabins — are reported on their own, never folded into the main house figure.
Keeping these out is not about downgrading the space; it is about comparing homes on the same basis. A buyer should be able to trust that the square-footage figure means finished, heated, above-grade living area and nothing else.
- Open porches, balconies, and decks — not enclosed living space.
- Unheated or three-season sunrooms — no permanent heat source.
- Unfinished basements and attics — bare, unfinished space.
- Garages, attached or detached — unfinished and unconditioned.
- Detached guest houses, sheds, and pool houses — reported separately.
What counts that people forget — and why the tax card differs
Just as important as the exclusions is what quietly does count. Closets, built-in wardrobes, and hallways are all part of the finished living area and belong in the total — they are heated, finished, above-grade floor space you walk through every day. Interior stairways count too, but only once: the standard counts the stair opening as area on the floor it descends from, so you never double-count the same steps on two levels. Interior wall thickness is included when you measure to the exterior walls.
This is also why your tax assessor's square footage rarely matches an appraisal. Assessors work from permits, older records, and their own local rules, and they may count or exclude spaces differently than ANSI does — sometimes including a finished basement in the headline number, sometimes measuring from the outside without the same adjustments. Neither figure is necessarily "wrong," they are answering slightly different questions. When precision matters, measure to a consistent standard rather than trusting whichever number is on file. Start by learning to measure a room accurately.