How to Calculate Square Footage of a Room or House
How to calculate square footage for rooms, L-shapes, and whole houses — including what counts as finished space in a listing, and a full worked example with conversions.
The base formula
For any rectangle:
Square footage = length (ft) x width (ft)
A 12 ft by 14 ft bedroom is 12 x 14 = 168 sq ft. Measure wall to wall at floor level, and record inches as decimals: 12 ft 6 in is 12.5 ft, not 12.6.
Convert inches by dividing by 12: 9 in = 0.75 ft.
Irregular rooms: split into shapes
Anything that is not a rectangle becomes a set of rectangles, triangles, and circles you add together.
- Rectangle: L x W
- Triangle: 0.5 x base x height
- Circle: 3.1416 x radius squared
- Trapezoid: 0.5 x (side A + side B) x height
Subtract permanent obstructions like a kitchen island or a structural column if you are buying flooring.
Worked example: an L-shaped living room
The room measures 20 ft along the long wall and 16 ft deep, with a 6 ft by 5 ft alcove cut out of one corner.
- Full rectangle: 20 x 16 = 320 sq ft
- Missing corner: 6 x 5 = 30 sq ft
- Actual area: 320 - 30 = 290 sq ft
Buying flooring? Add 10% for cuts and waste (15% for diagonal or herringbone layouts): 290 x 1.10 = 319 sq ft to order.
Common room sizes for reference
| Space | Typical size | Square footage |
|---|---|---|
| Small bedroom | 10 x 10 ft | 100 |
| Primary bedroom | 14 x 16 ft | 224 |
| Standard bathroom | 5 x 8 ft | 40 |
| Kitchen | 12 x 12 ft | 144 |
| Living room | 16 x 20 ft | 320 |
| Two-car garage | 20 x 20 ft | 400 |
What counts in a home's listed square footage
Real estate convention (ANSI Z765 in the US) counts finished, heated, above-grade living space measured from the exterior walls. Generally excluded:
- Unfinished basements, and in many markets finished basements too (listed separately as "below grade")
- Garages, even when finished
- Open porches, decks, and patios
- Attics with less than 7 ft of ceiling height, and any area under 5 ft of headroom
- Stairwell openings on the upper floor (the stair itself counts on the lower floor)
This is why an appraiser's number is often lower than what the tape measure inside your rooms suggests: interior measurements exclude wall thickness, exterior ones include it.
Converting to metric
1 sq ft = 0.092903 m squared, and 1 m squared = 10.7639 sq ft.
That 290 sq ft living room is 290 x 0.092903 = 26.9 m squared.
FAQ
How do you calculate square footage of a house? Measure each finished, heated room, calculate its area, and add them together — or measure the exterior footprint per floor and subtract garages and unfinished areas.
Does a garage count in square footage? No. Garages, unheated porches, and unfinished basements are excluded from listed living area, even if finished.
How many square feet is a 12x12 room? 144 square feet, or about 13.4 square meters.
Run the shapes automatically with the Square Footage Calculator or the general Area Calculator. Doing a repaint next? How much paint do I need turns those measurements into gallons.
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*Measure once, calculate right: use the Square Footage Calculator for multi-shape rooms.*