What square footage should I use for homeowners insurance?

For homeowners insurance, insurers typically want finished above-grade living area — the same number an appraiser would call GLA. Finished basements are sometimes included depending on your policy. The key is total finished area, not lot size or tax assessment square footage.

FAQ / Square footage for homeowners insurance

Coverage · 5 min read

Square Footage for Homeowners Insurance: What Number to Use

Insurance companies care about square footage for one reason: estimating what it would cost to rebuild your home. That number is not the same as your tax assessment, your Zillow listing, or even your appraisal GLA — though they overlap. Here is how to think about it.

Why square footage matters for insurance

Homeowners insurance covers the cost to rebuild, not the market value of your home. Insurers use square footage as the primary input to estimate reconstruction cost. An inaccurate square footage — too low or too high — directly affects whether your coverage is adequate.

Under-insured: If your insurer has a smaller square footage on file than your home actually is, your dwelling coverage limit may be too low to rebuild after a total loss.

Over-insured: If the number on file is too high, you are paying more in premiums than you need to.

Which square footage do insurers use?

Most homeowners insurance policies are based on finished above-grade living area — the same space an appraiser would call Gross Living Area (GLA) under ANSI Z765. That means:

Included: All finished floors above grade — main level, upper levels, finished attic space with adequate ceiling height
Usually included: Attached garage (sometimes at a lower per-square-foot rate)
Depends on policy: Finished basement — some policies include it, some exclude it or cover it at a lower rate
Excluded: Unfinished basement, crawl space, unheated/unfinished attic

Your insurer may also measure covered decks, detached garages, and outbuildings separately under "other structures" coverage.

Why the insurance number differs from the appraisal number

Appraisers measure GLA from the exterior following ANSI Z765. That includes the wall thickness on all sides. Some insurers measure net interior square footage instead — or use their own estimation tools. Even when both are measuring "finished above-grade area," minor methodology differences create a gap of a few percent.

In practice, the appraisal GLA is a reasonable starting point for insurance, but ask your insurer specifically what they include — particularly around finished basements and attached garages.

How to find the right number

The most reliable approach is to measure from a to-scale floor plan:

Get a floor plan — from a recent appraisal, your home builder, CubiCasa, or a scan service like iGUIDE or Matterport
Measure the above-grade finished floors using exterior wall dimensions (ANSI Z765 method)
Measure the garage and basement separately
Give all three numbers to your insurer and let them apply their coverage formula

Do not rely on county assessor records or Zillow square footage for insurance purposes — both are frequently wrong by 5 to 15 percent, sometimes more.

What if I haven't measured my home recently?

Many homeowners discover a mismatch when they file a claim. If you have renovated, added square footage, or converted a garage or basement, your insurance square footage is likely out of date.

A floor plan photo — even from a recent MLS listing, a permit drawing, or a quick photo of a builder sketch — is enough to get an accurate measurement. You do not need to hire an appraiser specifically for this.

Get an accurate measurement for your insurer

Upload a floor plan and measure above-grade living area, basement, and garage separately — in under two minutes.

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