Why is my house's square footage different from county records?

County figures are often old, estimated from exterior measurements or permits, and may not include additions, finished attics or later changes. They can also include space a listing or appraisal leaves out, such as a finished basement. Different methods and different dates are the usual causes, not a single mistake.

How do I calculate the value of a square footage difference?

Divide the price by the stated square footage to get the stated price per foot, then multiply by the difference. A $489,000 home stated at 2,150 square feet is $227.44 per foot; if it measures 1,987, the 163 square foot gap is about $37,073 at that rate. It sizes the gap; it isn't an appraisal.

How much of a square footage difference is normal?

There's no single accepted tolerance. Two careful measurements using the same method should be close, with small differences from rounding and how walls are measured. A gap of several percent usually has a cause you can find, such as a basement or garage included in one figure, or interior instead of exterior measurements.

Which square footage number is right?

The one measured to a stated method, with what's included written down. For homes, that's usually above-grade finished area measured to the outside of the walls, as in ANSI Z765-2021, which Fannie Mae requires for appraisals with interior and exterior inspections. A figure with no method or date behind it is the weakest.

Can I appeal my property taxes if the square footage is wrong?

Many assessors will correct a wrong record or hear an appeal, but the process, evidence and deadlines vary by county. Start by asking your assessor's office how they measured and what they need from you. For anything beyond a records correction, check with a local real estate attorney or tax professional.

Free calculator

Square Footage Discrepancy Calculator

Compare listed or county square footage with a measured figure: the difference, the percentage, and what it's worth at the price per foot.

Stated by

Stated square footage

sq ft

Measured square footage

sq ft

Your own measurement, an appraisal, or a plan you measured.

Price (optional)

Sale, list or assessed value, for the price per foot.

Result

Measured vs. listing

−163sq ft

−7.6% smaller than stated

Stated: 2,150 sq ft
Measured: 1,987 sq ft
$/sq ft at stated size: $227.44
$/sq ft at measured size: $246.10
Difference at stated $/sq ft: −$37,073.02

The dollar figure is the gap times the stated price per foot. It's a way to size the difference, not an appraisal or a measure of damages.

How it's calculated

Difference = measured − stated; percent = difference ÷ stated; value = difference × (price ÷ stated sq ft). A listing says 2,150 sq ft and you measure 1,987: that's 163 sq ft (7.6%) smaller. At $489,000 the stated rate is $227.44 per sq ft, so the gap is about $37,073 of floor area.

How to use the calculator

Choose where the stated figure came from, enter it, and enter the measured figure. Add a price (sale, list or assessed value) to see the price per square foot both ways and what the gap is worth at the stated rate. The percentage is always relative to the stated size, so a home 163 sq ft smaller than a 2,150 sq ft listing is 7.6% smaller.

A worked example

Step	Math	Result
Difference	1,987 − 2,150	−163 sq ft
Percent	−163 ÷ 2,150	−7.6%
Stated price per foot	$489,000 ÷ 2,150	$227.44
Measured price per foot	$489,000 ÷ 1,987	$246.10
Gap at the stated rate	163 × $227.44	$37,073

Why square footage figures disagree

Cause	What happens	Usual effect
Inside vs. outside measurements	Room sizes leave out walls, halls and closets.	Interior total is lower
Basement included	Finished below-grade space added to the total.	Stated figure is higher
Garage, porch or sunroom included	Space that isn't finished living area counted in.	Stated figure is higher
Two-story spaces counted twice	The opening counted on the upper floor as well.	Stated figure is higher
Additions or finished attics	Not yet in county records.	County figure is lower
Old, rounded or estimated records	Figures copied forward for years.	Either way

Most gaps come down to what was counted, not arithmetic. The guide to square footage discrepancies goes through each cause and how to spot it.

Comparing like with like

Before deciding a number is wrong, find out how it was measured. Fannie Mae requires ANSI Z765-2021 for appraisals with interior and exterior inspections: finished, above-grade area measured to the outside of the exterior walls, with garages, unfinished space and below-grade rooms reported separately. A listing might include a finished basement. A county record might be decades old. If you measure it yourself, use the same method as the figure you're checking, or the comparison tells you about methods, not the house.

Getting a measured figure

If you have a floor plan, FloorFigures measures it for free with ANSI Z765-style rules applied, and its compare tab shows the measured figure next to the listed or county size, with the percentage and price per square foot. See how to verify square footage for the other records to check, and property tax appeals for wrong square footage if the county figure is the problem.

Updated October 12, 2026 · FloorFigures

Questions

Why is my house's square footage different from county records?: County figures are often old, estimated from exterior measurements or permits, and may not include additions, finished attics or later changes. They can also include space a listing or appraisal leaves out, such as a finished basement. Different methods and different dates are the usual causes, not a single mistake.
How do I calculate the value of a square footage difference?: Divide the price by the stated square footage to get the stated price per foot, then multiply by the difference. A $489,000 home stated at 2,150 square feet is $227.44 per foot; if it measures 1,987, the 163 square foot gap is about $37,073 at that rate. It sizes the gap; it isn't an appraisal.
How much of a square footage difference is normal?: There's no single accepted tolerance. Two careful measurements using the same method should be close, with small differences from rounding and how walls are measured. A gap of several percent usually has a cause you can find, such as a basement or garage included in one figure, or interior instead of exterior measurements.
Which square footage number is right?: The one measured to a stated method, with what's included written down. For homes, that's usually above-grade finished area measured to the outside of the walls, as in ANSI Z765-2021, which Fannie Mae requires for appraisals with interior and exterior inspections. A figure with no method or date behind it is the weakest.
Can I appeal my property taxes if the square footage is wrong?: Many assessors will correct a wrong record or hear an appeal, but the process, evidence and deadlines vary by county. Start by asking your assessor's office how they measured and what they need from you. For anything beyond a records correction, check with a local real estate attorney or tax professional.

Skip the typing. Measure the plan.

Open the floor plan in FloorFigures and every room is measured for you, with the same math per room. Try it free on a sample plan; nothing is uploaded.