Square footage decides what you pay for flooring, how a home is listed and often what it is worth. Measuring a single rectangular room is easy; L-shaped rooms, closets, sloped ceilings and basements are where most mistakes happen. This guide shows how to calculate square footage step by step, how to handle odd shapes and what counts as finished living area in a listing.
The basic formula
Square footage is length times width, both in feet. A 12 ft × 14 ft bedroom has 168 sq ft. If you measure in inches, multiply and divide by 144: 150 in × 130 in = 19,500 sq in ÷ 144 = 135.4 sq ft. If you measure feet and inches, convert the inches to decimal feet first: 12 ft 6 in = 12.5 ft.
The square footage calculator does this for every room at once, in feet, inches, meters or centimeters, and adds waste and cost for flooring.
L-shaped and irregular rooms
- Sketch the room and split it into rectangles and triangles.
- Measure each part and calculate its area: rectangle = length × width, triangle = base × height ÷ 2.
- Add the parts, then subtract anything that should not be covered, such as a fireplace hearth or a kitchen island.
Example: an L-shaped living room of 13 × 13 ft plus a 7.5 × 6.5 ft dining nook is 169 + 48.75 = 217.75 sq ft. A bay window shaped like a trapezoid can be split into a rectangle and two triangles.
What counts as finished square footage
For flooring you need every square foot you will cover. For a home listing or an appraisal, many US appraisers follow the ANSI Z765 standard, which is stricter:
| Area | Counted as finished square footage? |
|---|---|
| Heated, finished rooms above grade | Yes, measured from the exterior walls |
| Ceiling height | At least 7 ft; with sloped ceilings, at least half of the room must reach 7 ft and areas under 5 ft are excluded |
| Finished basement (below grade) | Reported separately, not added to above-grade area |
| Garage, unheated porch, deck | No |
| Stairs | Counted on the level they descend from |
Rules differ between states, brokers and lenders, so for a sale or a mortgage check which standard is used. For buying materials, always use the interior measurements of each room.
From square footage to flooring
| Room area | +10 % waste | Boxes of 20 sq ft | Cost at $3.50/sq ft |
|---|---|---|---|
| 120 sq ft | 132 sq ft | 7 | $462 |
| 168 sq ft | 185 sq ft | 10 | $647 |
| 250 sq ft | 275 sq ft | 14 | $963 |
| 400 sq ft | 440 sq ft | 22 | $1,540 |
Use 10 % waste for straight layouts and about 15 % for diagonal or herringbone. Carpet is often sold by the square yard: divide square feet by 9.
Frequently asked questions
How do I calculate the square footage of a house?
Calculate each room or measure the outside walls of each floor, then add the floors. For listings, report finished above-grade area and the basement separately.
Do closets count in square footage?
Closets inside the heated living area are usually included in a home's square footage. For flooring, include them if you are covering them.
How many square feet is a 10 × 12 room?
120 square feet, or about 11.1 m².
How do I convert square feet to square meters?
Multiply by 0.0929. 200 sq ft is about 18.6 m². The other way, multiply square meters by 10.764.