Guide
Why Square Footage Differs From the Listing or County
Listing, county and appraisal square footage often disagree. The usual causes, which number is right, and how to check it yourself.
Updated · FloorFigures
Short answer
The numbers differ because each source measures differently and counts different spaces. A county record may include a finished basement or be out of date, a listing can repeat any source, and appraisers on Fannie Mae and Freddie Mac loans use ANSI Z765-2021, which counts only finished, above-grade area as living area. Trust the figure whose method you know (usually a recent appraisal), and measure if the gap matters: at $250 per sq ft, a 100 sq ft gap is $25,000 of asking price.
A house has one size, but it can have four or five published square footage figures: the listing, the county assessor's record, an appraisal, the builder's brochure and whatever a real estate website shows. They rarely agree. Often that isn't an error; it's different people measuring different things. Here's where each number comes from, which one to rely on, and how to check it yourself.
Why do square footage numbers differ?
There is no single legal standard for measuring a house in the US. ANSI Z765 is the national standard for single-family homes, but it's voluntary, and it says itself that it isn't meant to replace any legally required method. Fannie Mae and Freddie Mac require it for appraisals; no national rule requires it for listings or tax records. So each source uses its own method:
| Source | Where the figure usually comes from | How it's typically measured | What it tends to include |
|---|---|---|---|
| Listing (MLS) | The agent, the seller, the county record, a prior appraisal or the builder's plan | Whatever the source used; may or may not follow ANSI Z765 | Varies: sometimes one total that adds a finished basement to the main floors |
| County assessor | The assessor's records, often from permits, plans or an exterior measurement | The county's own method; may not be updated after remodels | Varies by county: finished basements and attics may be included, excluded or listed separately |
| Appraisal | The appraiser's own measurement, or a supplied floor plan for a desktop appraisal | ANSI Z765-2021 for Fannie Mae and Freddie Mac loans on single-family homes | Finished, above-grade area as living area; below-grade, garage and nonstandard areas reported separately |
| Builder | The plan drawings or a sales brochure | Calculated from the plans, not the finished house | Depends on the label: a living or heated figure, or a larger total that can add the garage and porches |
| Real estate websites | Usually the listing or the public record | Whatever the original source used | Whatever the original source included |
Fannie Mae has required ANSI Z765 for appraisals with effective dates on or after April 1, 2022, and Freddie Mac for appraisals on or after November 2, 2023 (one-unit properties, not apartment-style condos or co-ops). An appraisal older than that may have used another method. More in Fannie Mae's ANSI requirement.
The usual causes of a gap
A gap often traces back to one space that one source counted and another didn't:
| Cause | What happens | Which figure is higher |
|---|---|---|
| Finished basement | ANSI reports any level that is partly below grade separately; some listings and counties add it to the total | Listing or county |
| Garage conversion, sunroom or enclosed porch | Counted if it's finished for year-round use like the rest of the house; may be missing from a county record that wasn't updated | Either, depending on who updated |
| Room over the garage | Under ANSI it counts only if reached by a finished hallway or stairs; if you get there through the garage, it can only be listed separately | Listing or county |
| Low or sloped ceilings | ANSI needs a 7 ft ceiling; in a sloped room at least half the area must be 7 ft or more, and space under 5 ft never counts | Listing or county |
| Two-story foyer or great room | The opening is counted once, on the lower floor; adding it upstairs counts it twice | Whichever counted it twice |
| Room sizes added up | Rooms are measured inside the walls and skip halls and closets, so they total less than the outside measurement | The exterior figure |
| Plan versus as built | Figures from plans can differ from the house that was actually built | Either |
| Rounding and precision | Nearest inch versus nearest foot, and rounding the total | Either, by a few sq ft |
ANSI Z765 recognizes the plan problem directly: when finished area is calculated from plans, the measurer has to declare that it "may vary from the finished square footage of the house as built." See does a basement count and ceiling height rules for the details.
Which square footage should you trust?
Trust the figure whose method you know and can check. For a single-family house that is usually a recent appraisal for a Fannie Mae or Freddie Mac loan: the appraiser measured the house, followed a published standard, and reported above-grade and below-grade area separately. Two cautions: an appraisal from before April 2022 may not follow ANSI, and a desktop appraisal relies on a floor plan someone else supplied (Fannie Mae encourages ANSI for desktop appraisals but doesn't require it).
A listing figure is only as good as its source, so ask the agent where it came from. Colorado makes this routine: its Real Estate Commission's square footage disclosure form says whether the broker measured, by which method, or which source the number came from. A county figure exists to value the property for tax; it's a useful cross-check but not a measurement standard. A builder figure describes the plans.
Your own measurement, done the ANSI way, is as good as your tape and your care. If two careful measurements agree, that's the number.
How big a gap is normal?
There is no official tolerance. What you can do is ask what could explain the gap. Measurement precision moves a total very little: a 40' × 30' house measured 0.1 ft long on both sides comes out 40.1 × 30.1 = 1,207 sq ft instead of 1,200, a difference of 7 sq ft (0.6%). A gap of a few square feet is usually rounding. A gap the size of a basement, a bonus room or a porch is a definition difference. A gap you can't match to any space is the one worth questioning.
To see what a gap means in money, multiply it by the price per square foot. On a 2,000 sq ft listing at $250 per sq ft:
| Gap | Share of 2,000 sq ft | Gap × $250 per sq ft |
|---|---|---|
| 25 sq ft | 1.25% | $6,250 |
| 50 sq ft | 2.5% | $12,500 |
| 100 sq ft | 5% | $25,000 |
| 200 sq ft | 10% | $50,000 |
| 400 sq ft | 20% | $100,000 |
The gap also changes the price per foot. A $500,000 house listed at 2,000 sq ft is $250 per sq ft; if it measures 1,880 sq ft, the same price is $265.96 per sq ft. If you're comparing homes by price per foot, that's the number that moves your comparison. Run your own figures in the square footage discrepancy calculator or the price per square foot calculator.
How to check it yourself
- Collect every figure and its source: the listing, the county property record card, any prior appraisal and the builder's plan.
- Compare like with like: split each figure into above-grade, below-grade and garage if you can. Many gaps vanish once a basement is moved to its own line.
- Measure: from the outside walls, level by level, or from a floor plan with a checked scale. See how to measure a house.
- Explain the rest: match what's left to a specific space. If nothing fits, measure again or ask an appraiser.
The full walkthrough is in how to verify a home's square footage. If the county has it wrong, see property tax appeals; if a listing was wrong, see who is responsible.
Comparing figures in FloorFigures
FloorFigures is a free floor plan measuring tool that runs in your browser. Open the listing's floor plan or a builder PDF, trace the building outline (it leaves out the garage and porch), and it applies ANSI Z765-style rules: below-grade space on its own line, openings to the floor below subtracted, ceiling-height rules applied. The Compare tab sets your measured figure against the listed or county size and shows the difference, the percentage and the price per square foot. Nothing is uploaded.
Questions
- Why is my square footage different from county records?
- County assessors use their own local measuring methods, often record a house once from permits, plans or an exterior measurement, and may not update the record after an addition, a finished basement or a garage conversion. Some counties fold finished below-grade space into the total and others don't. Listings and appraisals may count those spaces differently, so the figures rarely match exactly.
- Which square footage is correct: the listing, the county or the appraisal?
- The most reliable figure is the one whose method you know. For a single-family house that is usually a recent appraisal for a Fannie Mae or Freddie Mac loan, because those appraisers must measure by ANSI Z765-2021 and report above-grade and below-grade area separately. Listing and county figures often don't say how they were measured. If the number matters to you, measure the house or have an appraiser measure it.
- Is a square footage discrepancy normal?
- Small differences are normal: measuring to the nearest inch versus the nearest tenth of a foot, rounding, and where the tape meets the wall can move a total by a few square feet. A gap about the size of a room usually means one source counted a space the other didn't, such as a finished basement, a bonus room or an enclosed porch. A gap you can't explain that way is worth measuring.
- How much is a square footage error worth?
- Multiply the gap by the price per square foot to see its scale: 120 sq ft at $250 per sq ft is $30,000. Treat that as a rough upper bound, not a valuation. Homes aren't priced purely by size, and appraisers typically adjust for differences in size at less than the average price per square foot.
- Does a finished basement count in square footage?
- Not in gross living area under ANSI Z765, the standard appraisers use for single-family homes: any level that is even partly below grade is reported as below-grade finished area, separately from above-grade living area. Listings and county records may still add it into a single total, which is one of the most common reasons the numbers differ.