The real estate and appraisal industries do not have any one common methodology or guideline for measuring residential square footage. Nor is a uniform standard for measuring a home required. Around 1996 a residential measurement standard became available; created by the ANSI (American National Standards Institute) However, most practitioners have never seen the entire document, nor can they describe the principles of the ANSI standard for measuring residential square footage. Even i have not se...

The real estate and appraisal industries do not have any one common methodology or guideline for measuring residential square footage. Nor is a uniform standard for measuring a home required. Around 1996 a residential measurement standard became available; created by the ANSI (American National Standards Institute) However, most practitioners have never seen the entire document, nor can they describe the principles of the ANSI standard for measuring residential square footage. Even i have not seen this document nor have had this standard taught in any class. To add to the confusion there is also an AMS (American Measurement Standard) method for residential measuring that an individual can go by!

Calculating residential square footage will depend upon which of these philosophies the person doing the measuring was taught and what local variations (of which there are hundreds) the individual factors into the measurments they are taking. An example of a local variation includes whether to include the staircase as part of the livable square feet, or whether or not to include the space beneath a staircase, or whether to include certain closets or alcoves in the total. Another variation is whether to measure around the exterior foundation only, or to measure exclusively from the interior where the thickness of the walls will affect the total. Bottomline, without a "required" methodology for calculating residential square footage everyone who measures the property will end up with a different total.

I've included a couple of links below to more information about this topic.

In the MLS listing it will show where they home square footage was taken from ie. appraisal district, appraiser or seller. You can double check what the appraisal district shows the square footage to be going to the website of that particular county and entering the address. Note: even the appraisal district can be off some.

I would have your Realtor double check with the listing agent to see where there square footage came from. If you put the home under contract the appraiser will...

In the MLS listing it will show where they home square footage was taken from ie. appraisal district, appraiser or seller. You can double check what the appraisal district shows the square footage to be going to the website of that particular county and entering the address. Note: even the appraisal district can be off some.

I would have your Realtor double check with the listing agent to see where there square footage came from. If you put the home under contract the appraiser will measure the square footage of the home. If you feel it is way off, you can also have your home inspector do a rough calculation of square footage. The best source of square footage will come from your appraiser who use specific measurements and not calculations provided online.

Hope that helps a little