Why the Square Footage Never Matches — CAD, Appraiser, and Floor Plan

A house I listed recently — 110 Cloudbridge Drive in League City — has three square footage numbers attached to it.

The appraisal district says 2,385. The measured floor plan from the 3D scan says 2,205. That's a 180 square foot gap — about 7.5% — on the same house, measured by people who both knew what they were doing.

Neither one is wrong. They're answering different questions. And if you don't know that going in, you will either overpay for space that isn't there or talk yourself out of a house over a discrepancy that means nothing.

The three numbers

The appraisal district number is gross area measured from the outside of the exterior walls, usually from a plat, a permit, or a drive-by. Nobody from the CAD has been inside your house. This is the number the MLS almost always publishes, because it's the only one that exists for every property in the county and it's free.

The floor plan number — the kind a 3D scan or a floor-plan service produces — is typically gross internal area. Measured wall face to wall face, inside. On a house with 2x4 framing, brick veneer, and a lot of exterior wall, that's a meaningful amount of thickness you just stopped counting.

The appraiser's number is the one that matters for your loan. Appraisers measure to a professional standard that counts finished, heated-and-cooled living area, applies consistent rules about what qualifies, and gets measured on site. It usually lands closer to the floor plan figure than to the CAD figure.

On my League City listing: 1,513 down and 872 up per the appraisal district, versus 1,421 and 784 measured internally. The gap is almost entirely wall thickness, and it's larger on the first floor because there's more exterior wall down there.

Why this matters more than it sounds like it should

Price per square foot comps get noisy. If you're comparing $/sq ft across listings, you're comparing numbers from inconsistent sources. Most come from the CAD, some come from a builder's plan, occasionally one comes from an actual measurement. That's not an apples-to-apples column even when it looks like one.

Appraisals come in on a different number than the listing. This is routine and usually harmless, because the appraiser applies the same standard to the comps. Problems start when a listing published an inflated figure from a source nobody disclosed.

Buyers feel misled. This is the real cost. Somebody reads 2,385, walks through, likes it, then sees 2,205 on the appraisal and wonders what else was oversold. Nothing was — but that conversation is now happening in week five instead of week one.

What a listing should do

Publish the number and the source. "2,385 sq ft per the Galveston Central Appraisal District" takes four extra words and eliminates the entire problem. Anyone who cares can go verify, and anyone who doesn't isn't surprised later.

If a house has a measured floor plan, publish that too. Two numbers with two sources reads as transparent. One number with no source reads as marketing.

What to do as a buyer

Ask where the number came from. If the answer is "the MLS," that means the appraisal district, which means gross exterior.

If square footage drives your decision, measure it. An appraisal will do it. So will a floor plan service, for a couple hundred dollars, before you spend money on an inspection.

Don't argue with the appraiser using the CAD number. They measure to a standard; the appraisal district estimates from the curb. That argument does not go where you want it to go.

Check the split, not just the total. On two-story houses the down/up allocation matters more than the total for how the house actually lives. A 2,385 with 1,513 down feels completely different from a 2,385 with 1,100 down.

What I'd actually tell you

Every listing in Texas publishes a number that came from a government office that never went inside. That's not a conspiracy, it's just the only universally available data.

Know which number you're looking at, ask for the source, and if the difference between 2,205 and 2,385 changes your answer on a house — measure it. That's a $200 question, not a $350,000 one.

Kelli Owens is a Texas REALTOR® with The KO Realty Group, brokered by The Sears Group. TREC License #616346. Square footage figures should be independently verified by any buyer relying on them.