Rectangles
Multiply length × width, both in feet. A 12 × 14 foot room is 12 × 14 = 168 square feet.
If you measured in inches, multiply and then divide by 144, because a square foot is 12 × 12 = 144 square inches. A 30 × 48 inch rug is 30 × 48 ÷ 144 = 10 square feet.
Odd shapes
Split the shape into rectangles, work out each one, and add them. A 12 × 14 foot room with a 5 × 6 foot alcove is 168 + 30 = 198 square feet.
For a triangle, multiply the base by the height and halve it: a triangle 6 ft along the base and 4 ft high is 6 × 4 ÷ 2 = 12 square feet.
Converting
| From | Do this | 168 sq ft becomes |
|---|---|---|
| Square feet to square yards | ÷ 9 | 18.7 sq yd |
| Square feet to square metres | × 0.0929 | 15.6 m² |
A square yard is 3 × 3 = 9 square feet, and a square foot is exactly 0.09290304 m².
Area, not volume
Square feet measure area. To fill a bed with soil or mulch, you also need the depth, which turns square feet into cubic feet; see cubic feet and bag sizes and mulch depth. Paint is bought by area; see paint coverage.