House Square Footage Calculator
Adding up a whole house is more than measuring rooms and stacking the totals. There are rules about what counts, where you measure from, and how finished space is treated, and those rules are the reason your county's number, the old listing, and a fresh appraisal can all disagree. The calculator below adds your rooms and levels into a single figure. The rest of this page explains how professionals arrive at the number that actually matters when you sell or refinance.
Gross living area vs total area
The number appraisers and agents care about is gross living area, usually written as GLA. It's the finished, heated, above-grade space you actually live in: bedrooms, bathrooms, kitchen, hallways, closets, and living spaces. It is not every square foot under the roof.
Total area, sometimes called gross building area, includes things GLA leaves out, like the garage, an unfinished basement, and covered porches. When a builder quotes a home as "3,200 square feet under roof," that's a total-area style number, and it's larger than the GLA a lender will use. Two homes can sit on the same footprint and report very different living areas depending on how much of that space is finished and heated. If you want a sanity check against typical homes, the guide on the average square footage of a house puts the numbers in context.
The ANSI Z765 standard
For decades there was no single rulebook for measuring a single-family home, which is why the same house could be advertised three different sizes. That changed when the big mortgage buyers adopted the ANSI Z765 standard, the American National Standard for measuring single-family residential square footage.
Fannie Mae made it mandatory first. Appraisals dated on or after April 1, 2022 for loans sold to Fannie Mae had to use ANSI-compliant measurement. Freddie Mac later adopted the same standard. If you're buying, selling, or refinancing with a conventional loan today, the appraiser is measuring your house to this rulebook, not by eyeballing the old tax card.
A few of the rules that trip people up:
- Ceiling height. Finished space needs at least 7 feet of clearance to count. In a room with a sloped ceiling, at least half the floor area has to be at 7 feet or more, and only the part above 5 feet counts at all.
- Above grade vs below grade. Any level that is partially or fully below ground gets reported separately as below-grade area, even if it's beautifully finished. A walk-out basement doesn't get folded into GLA.
- Round to the nearest whole square foot. Small stuff gets rounded, not fussed over.
Where you measure from: exterior vs interior
Under the ANSI standard, a house is measured to the outside of the exterior walls. The appraiser walks the perimeter and measures the building envelope, then subtracts open areas like a two-story foyer. This is different from how you'd measure for flooring, where you measure the inside of each room wall to wall.
That gap matters. Exterior measurement includes the thickness of the walls, so it produces a larger number than adding up interior room dimensions. On an average home the difference between exterior and interior measurement can run a few percent, easily 100 square feet or more. Neither is wrong, they answer different questions. For a floor covering estimate, measure interior. Start with the room square footage calculator and add the spaces up, or follow the pillar guide on how to calculate square footage.
Worked example: a whole two-story house
Here's how the total comes together on a real layout. This is an interior room count, the way you'd do it for flooring or a quick self-estimate, not the exterior appraisal figure.
First floor
| Room | Dimensions | Square feet |
|---|---|---|
| Living room | 16 x 20 | 320 |
| Kitchen | 12 x 15 | 180 |
| Dining room | 11 x 13 | 143 |
| Half bath | 5 x 6 | 30 |
| Hallway and entry | 6 x 18 | 108 |
| First-floor total | 781 |
Second floor
| Room | Dimensions | Square feet |
|---|---|---|
| Primary bedroom | 14 x 16 | 224 |
| Bedroom 2 | 11 x 12 | 132 |
| Bedroom 3 | 10 x 12 | 120 |
| Full bath | 8 x 10 | 80 |
| Hall bath | 5 x 9 | 45 |
| Landing and hall | 6 x 14 | 84 |
| Second-floor total | 685 |
Add the two finished levels: 781 + 685 = 1,466 square feet of gross living area. Notice what's not in the table. The attached garage, the unfinished basement, and the covered front porch are all left out, because none of them are finished, heated living space. If this home also had a finished basement, that space would be listed separately as below-grade area, not blended into the 1,466.
An appraiser measuring the same house from the outside would likely report a slightly higher number, maybe 1,520 to 1,580, because exterior measurement picks up the wall thickness and interior partitions. Same house, different method, and both are correct for their purpose.
What counts and what usually doesn't
Here's the quick reference for the spaces people argue about most.
| Space | Counts toward GLA? | Notes |
|---|---|---|
| Finished, heated rooms above grade | Yes | The core of GLA |
| Finished closets and hallways | Yes | Part of the living area |
| Finished basement | No | Reported separately as below-grade area |
| Unfinished basement | No | Excluded entirely |
| Attached garage | No | Not finished and heated to the home's standard |
| Attic (finished, 7 ft clearance) | Sometimes | Only the portion with 7 ft height, if half the floor qualifies |
| Attic (unfinished storage) | No | Excluded |
| Covered porch or deck | No | Not heated like the house |
| Three-season sunroom | No | Excluded unless heated and cooled year round to the home's standard |
| Open two-story foyer | Counted once | Floor area counts on the lower level only |
The garage is the one that starts the most fights, so it has its own explainer on whether a garage counts as square footage.
How stairs get counted
Staircases confuse people because a stair is technically floor area on two levels at once. The ANSI rule keeps it simple: stairs are counted as part of the level from which they descend, and the area underneath the stairs counts toward the lower level. So a staircase going from the first floor down to the basement counts in the above-grade first-floor area, while the space under those stairs belongs to the basement.
The one adjustment appraisers make is when the opening in the floor is bigger than the staircase itself. If a second-floor landing has a 10 by 10 opening (100 square feet) but the stair footprint is only 3 by 8 (24 square feet), the extra 76 square feet of open floor gets subtracted from the upper level, since it's open to the room below. For a normal straight-run stair where the opening matches the stair, there's nothing to subtract. You count the stairs once, on the floor they leave from.
Why appraisal, tax record, and listing numbers differ
Homeowners are surprised all the time when three sources give three sizes. It's rarely a single error. It's that each number was created for a different reason, by different people, at a different time.
- The county tax record is often decades old, copied from the original building plans, and measured under whatever local convention applied back then. It may still show an unfinished attic, or miss a permitted addition, or include space that was later changed.
- The listing (MLS) is entered by the agent. It might pull from the tax card, an old appraisal, a floor plan, or a tape measure walk. Sources vary, so listings drift from records.
- The appraisal measures the house as it stands today, to the ANSI rulebook, from the exterior. It's the number the lender trusts.
Redfin's guide on wrong square footage makes the same point, that public records and MLS listings pull from different sources and often don't match. What to do about it depends on which way it cuts. If you're selling and the tax record undersells your home, order a professional measurement or an appraisal and put the higher, documented number on the listing. If you're buying and the listing looks generous, ask the agent what's included, check it against the county record and the floor plan, and let the appraisal settle it. If your assessment overstates your home and inflates your tax bill, most counties have an appeal process where a measured floor plan is strong evidence. A difference of a few percent is normal and usually not worth chasing. A difference of several hundred square feet is worth documenting.
Common mistakes
- Counting the garage. It inflates your price per square foot and the appraiser will strip it back out.
- Counting the finished basement in the main number. Below-grade finished space is valuable, but it's reported separately, not blended into GLA.
- Double-counting the two-story foyer. The open space above the entry is not second-floor square footage.
- Trusting the old tax card. If you've finished or converted space, the record may be years behind reality.
Frequently asked questions
How do you calculate the square footage of a house?
Measure each finished, heated, above-grade room, multiply length by width, and add the rooms together, level by level. For an official figure, appraisers measure the exterior walls under the ANSI Z765 standard and exclude the garage, unfinished basement, and open two-story spaces. The two methods give slightly different numbers because exterior measurement includes wall thickness.
What is gross living area?
Gross living area, or GLA, is the finished, heated, above-grade space in a home: bedrooms, bathrooms, kitchen, and living areas. It excludes the garage, unfinished areas, and any level below grade, even if that level is finished. GLA is the number lenders and appraisers use to compare homes.
Why is my house a different size than the county says?
County and tax records are often old and were measured under different conventions, so they can include or exclude space that no longer matches the home. A current appraisal measures the house as it stands, using the ANSI standard. A difference of a few percent is common and usually not an error.
Does the basement count in a home's square footage?
Not in the main above-grade number. A finished basement adds real value, but under the ANSI standard any space that is partly or fully below grade is reported separately as below-grade finished area, not as part of gross living area.
Should I measure from the inside or the outside walls?
For an appraisal-style house total, measure the exterior walls, which is what the ANSI standard requires. For flooring, paint, or materials, measure the interior of each room wall to wall. Exterior measurement produces a larger number because it includes the wall thickness.
Do stairs count as square footage?
Yes. Under ANSI, a staircase counts in the finished area of the level it descends from, and the space underneath counts toward the lower level. Stairs are counted once, not on both floors. The only adjustment is when the floor opening is larger than the stairs, in which case the extra open area is subtracted from the upper level.
Does a sunroom count as square footage?
Only if it's finished and heated and cooled by a permanent system to the same standard as the rest of the house, and it sits above grade. A three-season or screened sunroom that isn't conditioned year round is excluded from gross living area and valued separately.
Sources
- Freddie Mac Adoption of the ANSI Measurement Standard, McKissock Learning
- ANSI Z765 and What Fannie Mae Made Mandatory, Aladdin Appraisal
- Navigating Stairs with ANSI, McKissock Learning
- Wrong Square Footage, Redfin
- Square footage discrepancy in county tax records and current listing, discussion thread
Related tools: Room Square Footage Calculator, the guide on whether a garage counts as square footage, the average square footage of a house, and the how to calculate square footage pillar. Browse the homepage for the full set of calculators.