The short answer
To calculate square footage, multiply the length by the width in feet. A 12 × 10 ft room is 120 square feet. For an L-shaped room, split it into two rectangles and add them; for a circle, multiply 3.1416 by the radius squared. Divide square feet by 9 for square yards, or by 10.764 for square metres.
Area formulas
| Shape | Formula |
|---|---|
| Rectangle or square | length × width |
| L-shaped room | (length₁ × width₁) + (length₂ × width₂) |
| Circle | 3.1416 × (diameter ÷ 2)² |
| Triangle | base × height ÷ 2 |
| Trapezoid | (top + bottom) ÷ 2 × height |
All measurements must be in the same unit. In US units, convert inches to feet before multiplying. Most flooring, paint and sod calculations use the floor or wall area, so measure wall to wall.
Worked example
An L-shaped living room: the main section is 12 × 10 ft and the alcove is 6 × 5 ft.
- 12 × 10 = 120 square feet
- 6 × 5 = 30 square feet
- Total: 150 square feet, or 16.7 square yards, or 13.9 square metres
Common room sizes
| Room size | Square feet | Square yards | Square metres |
|---|---|---|---|
| 10 × 10 ft | 100 | 11.1 | 9.29 |
| 10 × 12 ft | 120 | 13.3 | 11.15 |
| 12 × 12 ft | 144 | 16.0 | 13.38 |
| 12 × 15 ft | 180 | 20.0 | 16.72 |
| 15 × 20 ft | 300 | 33.3 | 27.87 |
| 20 × 20 ft | 400 | 44.4 | 37.16 |
Unit conversions
- 1 square yard = 9 square feet
- 1 square metre = 10.764 square feet
- 1 acre = 43,560 square feet
- 1 hectare = 10,000 square metres = 2.471 acres
Tips for measuring
- Measure at floor level, wall to wall, and round each measurement up to the nearest inch.
- Sketch the room first and write each measurement on the sketch; it makes irregular shapes much easier.
- Closets count if the flooring runs into them, so measure them separately and add them.
Frequently asked questions
How do I calculate square feet?
Measure the length and width in feet and multiply them. If a measurement includes inches, convert the inches to a decimal of a foot first by dividing by 12; 10 feet 6 inches is 10.5 feet.
How do I find the square footage of an irregular room?
Break the room into rectangles, triangles or circles, calculate each area separately, and add them together. Subtract any areas you are not covering, such as a fixed kitchen island.
How many square feet are in a square yard?
There are 9 square feet in a square yard (3 ft × 3 ft). Carpet is often priced per square yard, so divide square feet by 9.
How many square feet are in an acre?
One acre is exactly 43,560 square feet, or about 4,047 square metres.
How much extra flooring should I buy?
Add 5–10% for straight layouts and 10–15% for diagonal or herringbone patterns, which create more cut pieces.
Sources
Related calculators
About this calculator. Every formula on this page is tested against worked examples from the sources above before publishing. Results are estimates for planning; confirm with your supplier or local code.
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