What to measure
How to use the square footage calculator
- Pick the shape: rectangle, L-shape, triangle or circle.
- Enter the measurements in feet, inches, yards or meters. Changing one unit changes them all.
- For flooring or tile, add 10% waste. Add a price per square foot to get a cost estimate.
For a room with an odd outline, split it into simple shapes, run each one, and add the results.
The formulas
- Rectangle: length × width
- L-shape: length × width − cut-out length × cut-out width
- Triangle: base × height ÷ 2 (height measured square to the base)
- Circle: π × (diameter ÷ 2)²
- Square yards = square feet ÷ 9; square meters = square feet ÷ 10.764; acres = square feet ÷ 43,560
Worked example: 14 × 18 ft room
- 14 × 18 = 252 sq ft (28 sq yd, 23.41 m²)
- As an L-shape missing a 6 × 8 ft corner: 252 − 48 = 204 sq ft
- Flooring with 10% waste: 252 × 1.1 = 277.2 sq ft; at $3.50 per sq ft that is $970.20
Typical waste allowances
| Material | Extra to buy |
|---|---|
| Plank flooring | 10% (7% in large rooms) |
| Herringbone or chevron | 15% (12% in large rooms) |
| Carpet | Use the carpet calculator, which plans the roll cuts |
Frequently asked questions
How do I calculate square footage?
Multiply the length by the width, both in feet. A 14 × 18 ft room is 14 × 18 = 252 square feet. If you measured in inches, divide square inches by 144 to get square feet.
How do I find the square footage of an L-shaped room?
Measure the whole room as if it were a rectangle, then subtract the missing corner. A 14 × 18 ft room missing a 6 × 8 ft corner is 252 − 48 = 204 sq ft. Splitting it into two rectangles gives the same answer (14 × 10 + 8 × 8 = 204).
How much extra flooring should I buy?
About 10% for plank flooring and 15% for herringbone or chevron patterns, which waste more at the edges. Large rooms waste a little less, around 7% and 12%.
How is the square footage of a house measured?
For a mortgage appraisal, Fannie Mae requires the ANSI Z765-2021 standard. Finished area above grade is reported separately from basements, and a level counts as below grade if any part of it is. Unfinished space is listed on its own line, so a listing's figure is usually smaller than the sum of every room.
How do I convert square feet to square meters?
Divide square feet by 10.764. One square meter is 10.764 sq ft, so 20 m² is about 215 sq ft.
How many square feet are in a square yard?
Nine, since a square yard is 3 ft × 3 ft. Carpet and sod are often priced per square yard; the calculator shows both.
Sources
Formulas and defaults last reviewed October 30, 2026. How we check our math.