Area formulas
Rectangle = length × width Circle = π × (diameter ÷ 2)² Triangle = base × height ÷ 2
Measurements are converted to feet first, so the area comes out in square feet. For a triangle, the height is measured at a right angle to the base, not along a sloping side.
A round table or patio 10 ft across covers π × 5² ≈ 78.54 sq ft. A triangular corner with a 12 ft base and 9 ft height covers 12 × 9 ÷ 2 = 54 sq ft.
How to measure an L-shaped room
- Sketch the floor and split it into rectangles that don't overlap.
- Measure each rectangle wall to wall. Here: a main area of 14 ft × 12 ft and an alcove of 8 ft × 6 ft.
- Work out each area: 14 × 12 = 168 sq ft and 8 × 6 = 48 sq ft.
- Add them: 168 + 48 = 216 sq ft, which is about 20.07 m² or 24 sq yd.
- For flooring, add a waste allowance: 216 × 1.10 = 237.6, so buy at least 238 sq ft.
Write down feet and inches as decimal feet before multiplying. 12 ft 6 in is 12.5 ft, not 12.6 ft, because 6 inches is half a foot. If that's awkward, measure everything in inches and select inches in the calculator: 150 in × 126 in = 18,900 sq in, which is 131.25 sq ft.
Common room sizes
| Room (ft) | Square feet | Square meters | Square yards |
|---|---|---|---|
| 10 × 10 | 100 | 9.29 | 11.11 |
| 10 × 12 | 120 | 11.15 | 13.33 |
| 12 × 12 | 144 | 13.38 | 16 |
| 12 × 14 | 168 | 15.61 | 18.67 |
| 12 × 16 | 192 | 17.84 | 21.33 |
| 14 × 16 | 224 | 20.81 | 24.89 |
| 15 × 20 | 300 | 27.87 | 33.33 |
| 20 × 20 | 400 | 37.16 | 44.44 |
Conversion factors
1 ft = 12 in = 0.3048 m (exact) 1 sq ft = 144 sq in = 0.09290304 m² 1 sq yd = 9 sq ft
Area factors are the length factor squared, which is why 1 sq ft is 144 sq in, not 12. A room measured as 4 m × 3 m is 12 m², or about 129.17 sq ft. Carpet is often sold by the square yard, so divide square feet by 9.
Estimating material cost
Enter a price per square foot and the calculator multiplies it by the area. A 12 × 14 ft room at $3.50 per sq ft comes to $588. With a 10% waste allowance (184.8 sq ft), budget about $646.80. Flooring usually comes in boxes of a fixed coverage, so round up to whole boxes.