Why does the appraisal square footage differ from the tax record?

Appraisers measure exterior dimensions following ANSI Z765, producing an accurate GLA. Tax assessors use older records, interior measurements, or permit data that may never have been verified in the field. The appraiser's measurement is almost always more accurate.

FAQ / Appraisal square footage vs tax record

Appraisals · 5 min read

Appraisal Square Footage vs Tax Record: Why They Differ

It is common to see a 50, 100, or even 300 square foot gap between what the county tax record says and what a licensed appraiser measures. This is not a mistake — the two numbers are calculated differently, from different sources, at different times.

How tax assessors get their numbers

County tax records are built from a patchwork of sources: permit records, builder certificates of occupancy, field visits that may be years or decades old, and sometimes just estimates. Most assessors do not remeasure homes when they sell — they carry forward the number on file.

Tax records also vary in what they include:

Some counties use interior measurements — net livable area rather than exterior GLA
Some include finished basements in their total; others report them separately
Unpermitted additions are often absent from tax records entirely
Original construction records may have been inaccurate to begin with

How appraisers measure

Licensed appraisers follow ANSI Z765-2021 (for residential properties). They measure from the exterior, include all finished above-grade living space, and report finished below-grade areas separately. The measurement is done on-site or from a verified floor plan — not from county data.

The appraiser's number is almost always more accurate because it reflects an actual measurement of the current structure. Tax records reflect what was filed, often long ago.

Which number is right for buying or selling?

For a transaction involving a mortgage, the appraiser's number controls. Fannie Mae and Freddie Mac require lenders to use the appraiser's GLA for comparable sales adjustments. The tax record does not override the appraisal.

If you are a buyer or seller relying on the tax record to price a home, you may be working from a wrong number. A home that the county lists at 1,800 sq ft may appraise at 1,650 or 2,050 — both are common outcomes.

What if the appraisal looks wrong?

Appraisers make mistakes too — particularly in complex floor plans with multiple levels, bay windows, or attached structures. If the appraised square footage seems significantly off from what you know, you have options:

Request a copy of the sketch (appraisers are required to include one with residential reports)
Measure the sketch yourself using PlanSnapper or a similar tool to verify the appraiser's polygon matches the actual perimeter
If you find a discrepancy, request a reconsideration of value with your supporting measurements
For significant errors, you can request a second appraisal

Common gap sizes

In practice, the following gaps are typical:

Under 5%: Normal variance from measurement methodology (interior vs exterior)
5–15%: Suggests old records, a basement handling difference, or an addition that was not filed
Over 15%: Red flag — likely an unpermitted addition, a missing floor, or a data error worth investigating

Verify the square footage yourself

Upload the appraisal sketch or a floor plan and measure it in minutes. Know the number before closing.

Get Started