A house is rarely one simple rectangle, so its square footage is found by splitting the floor plan into smaller shapes and adding them up. This house square footage calculator keeps a running total for you: measure one section, name it, tap Add to total, and repeat until every part of every finished floor is included. Tick Subtract for spaces that should not count, such as the open area above a two-storey entryway.
Two ways to measure a house
1. From the outside (the standard method)
Professional measurements in the US usually follow ANSI Z765, a measuring standard that many appraisers use and that Fannie Mae has required for most appraisals since 2022. It measures each floor to the outside face of the exterior walls, so the wall thickness is included. Walk around the house with a long tape or laser, sketch the footprint, and split it into rectangles.
2. Room by room (from the inside)
Adding up the rooms gives a smaller number, because interior and exterior walls are not counted. That is perfect for estimating flooring or heating needs, but it will usually be 5–10% below the figure on a listing or appraisal.
How to calculate your home’s square footage
- Sketch each floor and split it into rectangles (plus triangles or trapezoids for angled walls).
- Measure each section to the outside of the exterior walls and add it to the total, naming it, e.g. “Main floor – front”.
- Repeat for each finished floor above ground level.
- Subtract openings to the floor below, such as a two-storey foyer, because their floor area is already counted downstairs.
- Report the basement separately. Finished space that is partly or fully below ground is normally listed apart from the above-grade total.
- Leave out garages, unfinished areas, and porches or decks.
What counts as finished square footage?
| Space | Counted in above-grade living area? |
|---|---|
| Finished, heated rooms above ground | Yes |
| Hallways, closets and stairs | Yes – stairs are counted on the floor they lead down from |
| Finished attic with enough headroom | Usually yes, if it is finished and reached by a permanent stair |
| Finished basement | Reported separately as below-grade area |
| Garage (attached or detached) | No |
| Porches, decks and patios | No |
| Open-to-below space (two-storey foyer) | No – only the floor below is counted |
| Unfinished storage and utility areas | No |
Local practice varies, so check what your appraiser, agent or county assessor uses before you compare figures.
Worked example: a two-storey house
- Main floor, main block: 40 × 30 ft = 1,200 sq ft
- Main floor, rear bump-out: 12 × 8 ft = 96 sq ft
- Upper floor: 40 × 26 ft = 1,040 sq ft
- Subtract open-to-below foyer: 10 × 12 ft = −120 sq ft
- Garage (22 × 22 ft): not included
Total above-grade living area: 1,200 + 96 + 1,040 − 120 = 2,216 sq ft (205.9 m²).
Price per square foot
Price per square foot is the sale price divided by the living area. A home that sells for $450,000 with 2,216 sq ft works out at $450,000 ÷ 2,216 = $203.07 per sq ft. Enter a price per square foot in the calculator to go the other way and estimate a value or a building cost. The figure is only meaningful when you compare similar homes in the same area, because location, age and condition matter as much as size.
Common house sizes
| House size | Square metres | Square yards | Single-storey footprint, e.g. |
|---|---|---|---|
| 1,000 sq ft | 93 | 111 | 40 × 25 ft |
| 1,500 sq ft | 139 | 167 | 50 × 30 ft |
| 2,000 sq ft | 186 | 222 | 50 × 40 ft |
| 2,500 sq ft | 232 | 278 | 50 × 50 ft |
| 3,000 sq ft | 279 | 333 | 60 × 50 ft |
Frequently asked questions
Does square footage include the garage?
No. Garages are not part of a home’s finished living area, even when they are attached and insulated. They are usually listed separately.
Does a finished basement count as square footage?
Under the ANSI Z765 standard, finished space that is partly or fully below ground is reported separately from the above-grade living area. Some listings show a combined figure, so check how a number was calculated before comparing homes.
Do you measure a house from the inside or the outside?
Official measurements are taken from the outside of the exterior walls. Measuring room by room from the inside gives a smaller number because the walls are left out.
How can I find my home’s square footage without measuring?
Check your county assessor’s property records, a past appraisal, the original building plans or an old listing. These figures are not always accurate, which is why measuring yourself is worthwhile.
Are stairs included in square footage?
Yes. Under ANSI Z765, a staircase is counted once, on the floor it descends from.
Why is my measurement different from the listing?
Common reasons are interior versus exterior measuring, a basement being included or excluded, open-to-below spaces being counted, or simple rounding. Small differences of a few percent are normal.
How accurate does my measurement need to be?
ANSI Z765 asks for measurements to the nearest inch or tenth of a foot, with the final total rounded to the nearest whole square foot. For everyday planning, measuring to the nearest inch is plenty.