“How many square feet is the house?” has a different answer from “how much floor is there”, and the difference is a standard: ANSI Z765, the square-footage method Fannie Mae has required for appraisals since 1 April 2022. This page works a house out that way.
Three things surprise people, and all three are in the standard:
- A finished basement is not added to the upstairs. No statement of a house’s finished square footage can be made without the clear and separate distinction between above-grade and below-grade areas — and a level counts as below grade if any part of it is, however it is finished and whatever its windows are like.
- Ceiling height decides what counts. Finished area needs 7 ft of ceiling (6 ft 4 in under beams, ducts and other obstructions, and no requirement under stairs). Where the ceiling slopes, at least half of the room must be 7 ft or higher, and no part under 5 ft counts at all. A room that fails the half test is not finished square footage — it is reported separately.
- Garages and unfinished space are not square footage, however they are fitted out, and a finished room you can only reach through an unfinished one is not either. A finished room attached to the house with no way in from inside it is reported on a line of its own, as noncontinuous finished area.
The standard also says how it is measured: at floor level, to the exterior finished surface of the outside walls for a detached house, or to the centerlines between houses where appropriate for an attached one. An opening down to the floor below is not counted, except that the stair treads and landings descending through it are counted on the floor they descend from, up to the area of the opening. The reported figure is rounded to the nearest whole square foot — or, in metric, to the nearest 0.1 m².
Already measured the rooms? Work them out on the calculator first and the totals can be carried over; then put each room on its own level. Rooms measured inside the walls add up to less than the same house measured outside. For every rule with a worked example and drawings to scale, see how to measure the square footage of a house. What this page will not do is add the two figures together for you.
On the source. The rules here were taken from Fannie Mae’s Selling Guide and its ANSI FAQ, which require the standard and restate parts of it, from an Appraisal Institute chapter’s published slides, and from the standard’s free 2020 public draft. The official copy of ANSI Z765-2021 has not been bought yet; until it has, every rule on this page is cited on the methodology page with where it was read, and the ones we could not verify are named as such.