House square footage calculator: in short
Add up the square footage of every finished, above-grade room on each floor. Keep garages, porches and basements on their own lines, because appraisers list them apart from the gross living area.
What gross living area means
Gross living area (GLA) is the finished living space of a house above ground. In the US, ANSI Z765 is the standard way to measure it, and Fannie Mae requires it for appraisals with an effective date on or after April 1, 2022.
Floor by floor: an example
The house is listed as 1,800 sq ft, with the basement and the garage mentioned separately.
| Part of the house | Square feet | In the GLA? |
|---|---|---|
| Main floor, finished | 1,100 | Yes |
| Second floor, finished | 700 | Yes |
| Basement, finished | 900 | No, below grade |
| Garage | 440 | No |
| Gross living area | 1,800 |
Basements and attics
If any part of a floor is below ground, the whole floor counts as below grade and stays out of the GLA, even when it is finished.
A finished attic counts when you reach it by a permanent stair and at least half of it is 7 ft high or more. Parts lower than 5 ft never count.
Outside or inside measurements
ANSI Z765 measures the outside of the exterior walls, so the walls are part of the square footage. Adding up rooms measured inside gives a smaller number. Use the inside number for flooring and furniture, and the outside number to compare with a listing.
Using the calculator for a house
Add the rooms of one floor to get that floor's total, then the next floor. The editor keeps floors, finished and unfinished space and below-grade areas apart and makes a GLA report.
Figure 1. One floor of 25 × 17 ft. The rooms add up to 425 sq ft.
Sources
- ANSI Z765-2021, Square Footage: Method for Calculating, Home Innovation Research Labs · Checked against the source on September 24, 2026
- ANSI Z765 frequently asked questions, Home Innovation Research Labs · Checked against the source on September 24, 2026
About this page · Written by the Squaremetry team, based on ANSI Z765-2021, Square Footage: Method for Calculating and ANSI Z765 frequently asked questions. Last checked on September 26, 2026. Found a mistake? Send us a message.