The Square Footage Listed in MLS Is Often Wrong — Here's What Buyers Need to Know

An appraiser posted something on X last week that should make every home buyer stop and think. He had just finished measuring a three-unit investment property. Tax records and the MLS listing both said the building was nearly 4,000 square feet. His tape measure said 2,200.

That’s a 1,800 square foot gap. It’s not a typo. It’s the kind of discrepancy that, depending on the local market, can represent $300,000 or more in perceived value — gone the moment a competent appraiser shows up with a measuring wheel.

The appraiser’s takeaway was blunt: “Don’t always rely on tax records or MLS information or the listing agent.”

He’s right. And the problem is far more common than most buyers realize.

Why Square Footage Numbers Are Often Wrong

Most real estate agents don’t measure homes themselves. That’s not laziness — it’s a liability issue. If an agent publishes a measurement and it turns out to be wrong, they can face fines from the MLS and potential lawsuits from buyers who overpaid. So agents do what seems safe: they copy the number from tax records or from a previous MLS listing.

The trouble is, those numbers are often wrong too.

County assessors typically collect square footage data from building permits, old surveys, or aerial estimates. They rarely enter the home. A homeowner who converted a basement, added a sunroom, or enclosed a carport may have done so without pulling a permit — meaning none of that additional space ever made it into official records. Meanwhile, an uncounted addition gets measured by someone decades later, and suddenly a 1,900-square-foot house looks like 2,600 on paper.

The other direction happens too. A home built with an attached garage in 1987 got recorded at total enclosed area. In some markets, that garage square footage gets copied forward across every listing and tax record for 35 years — even though garages don’t count as livable space under ANSI standards. The buyers shopping that home in 2026 are comparing it to other homes using a number that’s been inflated since Reagan was president.

When one wrong listing propagates into the comps that appraisers use, the error compounds. The North Carolina Real Estate Commission documented a case where a listing agent’s wrong figures spread through several comparable sales. Each comp had square footage errors of 6 to 7 percent — small enough not to trigger immediate suspicion, large enough to meaningfully affect pricing.

What This Costs Buyers in Real Terms

The financial math is straightforward and unpleasant.

In a market where homes are priced at $175 per square foot, a 100-square-foot error means a $17,500 difference in what a fair offer should look like. Authority Appraisals in St. Louis documented this clearly: at $200 per square foot, being 150 square feet off the actual size means buyers are working from a valuation that’s $30,000 too high.

At the higher end, the numbers get genuinely alarming. Real Estate Magazine Canada reported a scenario where a home had an advertised square footage roughly 400 square feet above what it actually measured, in a market with a $350-per-square-foot average. The price differential: $140,000.

About 15% of real estate contracts are terminated because of appraisal issues, and square footage discrepancies are a significant driver of those failures. A buyer who falls in love with a house, spends money on inspections, negotiates an offer, and then gets an appraisal that corrects the square footage downward is in a difficult spot. They either renegotiate, eat the difference, or walk away after weeks of wasted time and money.

A first-time buyer in Stouffville, Ontario experienced this firsthand. Their agent told them the home was approximately 2,100 square feet. The appraisal came back at 1,450. The buyer went to court and won rescission of the purchase agreement — which is an outcome, but not a fun one. The deal fell apart, the buyer lost months of their life, and the whole mess was caused by a number nobody bothered to verify.

The Specific Ways Square Footage Goes Wrong

Understanding how errors get introduced helps buyers know where to push back.

Relying on outdated MLS data. When an agent pulls up comps or prior listings for a property, they’re often copying numbers from sales that happened years ago. Those old numbers may have been wrong to begin with, and any changes to the home since then certainly weren’t captured.

Tax assessors don’t come inside. County appraisal districts use external measurements, permits, and aerial data. They don’t knock on the door and walk through with a measuring tape. An enclosed porch, a finished attic, a converted garage — all of these are likely missing from tax records unless the homeowner filed updated permits.

Garages and unfinished basements get counted. ANSI standards for gross living area (GLA) require spaces to be above grade, heated, and finished. Basements — even finished ones — don’t count as GLA in most measurement standards. Garages certainly don’t. But plenty of listings include them anyway, either through honest misunderstanding or deliberate inflation.

Unpermitted additions are invisible to records. Additions built without permits don’t show up anywhere official. An appraiser working from tax records won’t know about the 400-square-foot addition the previous owner built in 2015. But when a buyer pays a price that assumed 2,800 square feet and the appraiser finds 2,400, the deal is suddenly in trouble.

How to Protect Yourself Before You Make an Offer

The most important thing buyers can do is treat the listed square footage as a starting point for verification, not a settled fact.

Ask for the source. Your agent should be able to tell you where the square footage came from. If the answer is “tax records,” that’s a yellow flag. If the answer is “measured by an appraiser” or “measured by the listing agent using ANSI standards,” that’s better — though still worth verifying.

Pull the permit history. Most counties make permit records available online or at the building department. A home that has had additions, conversions, or significant remodels should have associated permits. If the work was done but no permits were pulled, you’re looking at unpermitted space that may or may not count toward livable area — and which could create problems with financing, insurance, or local code compliance.

Compare tax records to the listing. If the county assessor has the home at 1,800 square feet and the MLS listing says 2,400, that gap deserves an explanation. Ask for it. Sometimes the difference reflects above-code improvements that got reassessed; sometimes it’s inflated marketing. You need to know which before you make an offer.

Use the inspection period strategically. A good home inspector won’t necessarily measure every room, but they’ll walk the entire property. If you see a finished space the inspector flags as lacking permits or proper egress, that’s square footage that might not appraise as livable area. Some buyers hire a separate appraiser during the inspection period specifically to get an accurate measurement before they’re committed.

Understand what the appraisal will say. Even if you’re comfortable with the discrepancy, your lender isn’t. A mortgage is based on appraised value, and an appraiser who measures the home and comes up with a lower square footage will recalculate comparable sales accordingly. The loan amount can change. In a worst case, the deal falls through because the appraisal doesn’t support the purchase price.

Why Your Agent’s Skills Matter Here

A lot of buyers shop for homes using online portals that aggregate MLS data. The square footage shown on Zillow, Redfin, and Realtor.com is usually whatever the listing agent entered — which, as we’ve established, is often copied from tax records without verification.

An experienced buyer’s agent knows to flag these inconsistencies early. They’ll pull permit history, compare multiple sources, notice when finished basement square footage appears to be inflated into the living area number, and know when to push for written seller disclosure about additions and renovations.

MLS rules require accurate information, and listing agents who publish wrong square footage can face fines of $200 to $1,500. But fines only happen after the problem surfaces — usually after you’ve already made an offer, ordered inspections, and gotten emotionally attached to the house.

The cleaner path is a buyer’s agent who catches the discrepancy before any of that happens. Not every agent does this proactively. The ones who do are worth finding.