How to Calculate Square Footage of a Room or House
Calculate square footage for rooms, L-shaped spaces, circles and triangles: measure, multiply, add the parts and allow for waste on flooring or paint.
By Awais, Founder and editor-in-chiefPublished
To calculate square footage, measure the length and width in feet and multiply them. A room 12 feet by 15 feet is 12 × 15 = 180 square feet. For an L-shaped or irregular space, split it into rectangles (and the odd triangle or circle), work out each area, and add them up.
That’s all there is to it. The details that matter are measuring accurately, converting inches properly, and adding enough extra when you buy materials. The square footage calculator adds up several sections and works out cost per square foot.
Rectangles and squares
Measurements in feet and inches. Convert inches to a decimal of a foot by dividing by 12 before you multiply.
Example: a bedroom 11 ft 6 in by 13 ft 9 in.
- 11 ft 6 in = 11 + 6 ÷ 12 = 11.5 ft
- 13 ft 9 in = 13 + 9 ÷ 12 = 13.75 ft
- Area = 11.5 × 13.75 = 158.1 sq ft
Don’t multiply 11.6 × 13.9: “11 ft 6 in” is 11.5 feet, not 11.6.
| Inches | Feet | Inches | Feet |
|---|---|---|---|
| 1 | 0.083 | 7 | 0.583 |
| 2 | 0.167 | 8 | 0.667 |
| 3 | 0.25 | 9 | 0.75 |
| 4 | 0.333 | 10 | 0.833 |
| 5 | 0.417 | 11 | 0.917 |
| 6 | 0.5 | 12 | 1 |
Measurements in metres. Multiply in metres to get square metres, then multiply by 10.764 to get square feet. A room 4 m × 5 m is 20 m² = 215.3 sq ft.
L-shaped and irregular rooms
Split the space into rectangles that don’t overlap.
Example: an L-shaped living area. The long part is 20 ft × 12 ft. A dining nook sticks out from one side, 10 ft × 8 ft.
| Section | Size | Area |
|---|---|---|
| A: main room | 20 × 12 ft | 240 sq ft |
| B: dining nook | 10 × 8 ft | 80 sq ft |
| Total | 320 sq ft |
Another way to do the same shape: measure the whole bounding rectangle and subtract the missing corner. Both give the same answer, and doing it both ways is a good check.
Triangles, circles and other shapes
| Shape | Formula | Example |
|---|---|---|
| Triangle | base × height ÷ 2 | 10 ft base, 6 ft high: 30 sq ft |
| Circle | 3.1416 × radius² | 8 ft diameter (4 ft radius): 50.3 sq ft |
| Half circle (bay, patio) | 3.1416 × radius² ÷ 2 | 4 ft radius: 25.1 sq ft |
| Trapezoid | (side a + side b) ÷ 2 × height | 10 and 14 ft parallel sides, 8 ft apart: 96 sq ft |
For anything more complex, the area calculator handles each of these shapes and more.
Square footage of a house
For a whole home, add up the rooms, or measure the outside walls and work out the footprint of each floor. Two things to know:
- Listing square footage in the US usually means finished, heated living area, measured to the outside of exterior walls. Garages, unfinished basements, open porches and attics are usually listed separately. The ANSI Z765 standard, widely used by appraisers, sets out these rules.
- Room-by-room totals come out smaller than the listed figure, because they leave out wall thickness, hallways, closets and stairs.
So a house listed at 2,000 sq ft might measure only 1,750–1,850 sq ft if you add up the rooms. Neither number is wrong; they measure different things.
In Pakistan and India, plot area (in marla, kanal or square yards) and covered area (built-up floor area) are different numbers. Our guide to marla and kanal in square feet explains the plot units, and the land area converter converts between them.
Buying materials: add a waste allowance
Cuts, pattern matching and breakage mean you always need more than the bare area. Typical allowances:
| Material | Extra to buy |
|---|---|
| Laminate or vinyl plank, simple room | 5–10% |
| Tile, straight lay | 10% |
| Tile, diagonal or herringbone | 15–20% |
| Carpet | 10% (more for patterned carpet) |
| Sod or turf | 5–10% |
Example: 320 sq ft of laminate with 10% extra = 320 × 1.10 = 352 sq ft. If boxes hold 22 sq ft, you need 352 ÷ 22 = 16 boxes.
Paint uses wall area, not floor area. Work out each wall as width × height, subtract large windows and doors (about 20 sq ft per door and 15 per window is a common rough figure), then divide by the coverage on the tin, typically 350–400 sq ft per US gallon per coat.
Concrete and gravel need volume, not just area: area × thickness. A 10 × 12 ft patio 4 inches thick is 120 × (4 ÷ 12) = 40 cubic feet, about 1.48 cubic yards. The concrete calculator does the conversion and adds waste.
Cost per square foot
If flooring costs $3.80 per sq ft and installation $2.50, for 352 sq ft: 352 × (3.80 + 2.50) = $2,217.60.
To compare homes, divide the price by the square footage: a $420,000 house of 1,950 sq ft is $215 per sq ft. Only compare homes measured the same way.
Measuring tips
- Use a laser measure or a steel tape, not a cloth tape.
- Measure wall to wall at floor level, ignoring skirting boards for flooring.
- Measure twice in different places: rooms are rarely perfectly square.
- Sketch the room and write measurements on the sketch as you go.
- Round up to the next inch when buying materials, not down.
FAQ
How do I calculate square footage of a room?
Measure the length and width in feet and multiply. A 10 ft × 12 ft room is 120 sq ft. If you have inches, convert them to decimal feet by dividing by 12 first.
How do I convert square metres to square feet?
Multiply by 10.764. 50 m² is 538.2 sq ft. To go the other way, divide square feet by 10.764 (or multiply by 0.0929).
Do closets and bathrooms count in square footage?
In a home’s total finished area, yes, as long as they’re finished and heated. When buying flooring for a room, include the closet only if you’re flooring it too.
How many square feet is a 12 × 12 room?
144 sq ft. Add 10% for flooring waste and you’d buy about 158 sq ft of material.