TL;DR
Your square footage differs from the town records because the assessor's figure often comes from old or rough data and a different method than the ANSI Z765 standard appraisers use. Before you list or refinance, get an accurate measurement so your number matches what the buyer's appraiser will confirm.
Your home's square footage differs from the town records because the assessor's number and an appraiser's measurement often come from different methods and different eras. The town's figure may predate a renovation, rely on a rough or exterior measurement, or count space differently than the ANSI Z765 standard that appraisers must follow. When the buyer's appraiser measures to that standard, the result can differ from the town's number by enough to matter in a sale, which is why settling it early protects the transaction.
Why is my square footage different from the town records?
Because the assessor and the appraiser measure for different purposes with different methods. The town's job is mass valuation, often from records or exterior dimensions, and its figure may be old or rough. An appraiser measures your specific home to the ANSI Z765 standard, which counts gross living area precisely, so the two numbers often disagree.
The town's job is mass valuation, often from records or exterior dimensions, and its figure may be old or rough, which is why town records and actual home measurement often disagree.
An appraiser measures your specific home to the ANSI Z765 standard, which counts gross living area precisely, so the two numbers often disagree, as explained in the ANSI Z765 standard Fannie Mae made mandatory.
The assessor's figure was never intended to be the number a transaction relies on.
Which number is correct?
The ANSI Z765 measurement is the standard that governs how gross living area is calculated for appraisals, and it is the one the buyer's lender appraiser will apply. That makes it the number that matters in a sale or refinance, regardless of what the town card says.
A professional measurement to that standard gives you a figure you can advertise with confidence.
What counts toward square footage, and what doesn't?
Under ANSI Z765, gross living area is finished, above-grade space that meets ceiling-height and access rules. Below-grade space, such as a finished basement, is counted separately, and converted areas like attics and enclosed porches only count when they qualify. This is why a home can feel larger than its official GLA.
Below-grade space, such as a finished basement, is counted separately, and converted areas like attics and enclosed porches only count when they qualify, a rule detailed in the finished basement question and below-grade square footage in Greater Boston.
Getting each space categorized correctly is what prevents a mid-transaction dispute.
Why does the difference matter when I sell?
Because buyers and their agents calculate price per square foot and cross-check your listing against the town card and the appraisal. If your advertised figure is contradicted by the buyer's appraiser, the price the buyer relied on is suddenly wrong, and the deal can stall or renegotiate at the worst moment.
Settling the number before you list, on your timeline, avoids that surprise entirely.
Assessor's figure vs. ANSI measurement
FactorTown / assessor recordANSI Z765 measurementPurposeMass valuationPrecise gross living areaMethodOften records or exteriorStandardized, on-siteCurrencyMay predate renovationsReflects the home todayUsed by buyer's lenderNoYes
Before you list or refinance, get an accurate ANSI-compliant measurement so your number matches what the buyer's appraiser will confirm. Aladdin Appraisal provides professional measurement services across Greater Boston. This is general information; for your property, order a measurement or appraisal.
Aladdin Appraisal provides professional measurement services across Greater Boston, including ANSI-compliant home measurement in Lexington and throughout Middlesex County.
FAQ
Why is my square footage different from the town records?
Because assessors and appraisers measure differently. The town's figure is often old or based on exterior or record data, while appraisers measure your specific home to the ANSI Z765 standard, so the two frequently disagree.
Which square footage is the correct one for selling?
The ANSI Z765 measurement, because it is the standard the buyer's lender appraiser applies. That makes it the number that matters in a sale or refinance, regardless of the town card.
Does a finished basement count toward square footage?
Not toward above-grade gross living area. Under ANSI Z765, below-grade space like a finished basement is counted and valued separately, which is a common source of confusion.
Should I get my home measured before listing?
Yes. An accurate measurement before you list settles the number on your timeline and ensures it matches what the buyer's appraiser will confirm, avoiding a mid-transaction dispute.
About the author: Adam Wiener is the principal appraiser and owner of Aladdin Appraisal, a certified Massachusetts real estate appraisal firm serving Greater Boston across Middlesex, Suffolk, and Norfolk counties. Reach the team at (617) 517-3711 or info@aladdinappraisal.com.
NAP: Aladdin Appraisal | 187 Auburndale Ave, Auburndale, MA 02466 | (617) 517-3711 | info@aladdinappraisal.com | https://www.aladdinappraisal.com | Service area: Greater Boston across Middlesex, Suffolk, and Norfolk counties, MA
This article is general information, not legal, tax, or valuation advice for your specific property. For a formal opinion of value, order an appraisal; for legal or tax questions, talk to your attorney or tax professional.
