County says one number, the MLS another, the owner a third. Type the numbers you have. See which one to trust, why they differ, and how to get the right one.
$
Number to trust most right now
0 sqft—
Biggest gap
0 sqft
Gap × $/sqft
$0
Each source, ranked by trust
Trust scores are our rule of thumb from how each number is made, not an official rating. Only a measurement to a standard (ANSI) tells you the real number.
Why the numbers don't match
How to get the most accurate number
What counts, what doesn't
The standard appraisers use (ANSI Z765) works like wrapping a tape around the outside of the house. Then you take out what isn't real living space.
Rough check with a tape measure
Measure the outside walls of each box-shaped part of the house, in feet. Skip the garage and porch. Two-story? Add a row for the upper floor.
Your rough total0 sqft
Many people get this wrong:"The county number is official, so it's the right one." No. The assessor keeps it for taxes, and it can be decades old. It often misses an addition, or still counts a room that was changed. Official doesn't mean measured.
One more:A bigger number isn't a win for the seller. If an appraiser measures 150 sqft less, the appraisal can come in low, and someone has to cover the gap in cash.
"Approximate" doesn't cover everything:In a California case (Furla v. Jon Douglas Co., 1998) the listing said about 5,500 sqft and the home was well under. The court let the buyer's claim go on: a gap over 20% isn't minor, even with an "approximate" label.