How to calculate square footage
| Shape | Formula |
|---|---|
| Rectangle or square | Length × Width |
| Circle | 3.1416 × (Diameter ÷ 2)² |
| Triangle | Base × Height ÷ 2 |
Worked example
A patio 20 ft long and 10 ft wide is 20 × 10 = 200 sq ft. That's 22.2 square yards or 18.6 square meters.
Irregular shapes
Split the space into simple shapes, work out each one, then add them together. An L-shaped yard is two rectangles, which is what the second-area fields above are for. A rounded bed can often be treated as a rectangle plus half a circle.
Unit conversions
| From | To | Multiply by |
|---|---|---|
| Square feet | Square yards | ÷ 9 |
| Square feet | Square meters | × 0.0929 |
| Square feet | Acres | ÷ 43,560 |
| Square inches | Square feet | ÷ 144 |
Measuring in inches? Divide each measurement by 12 to convert it to feet before multiplying.
Frequently asked questions
How do I calculate square feet?
Multiply length by width in feet. A 12 × 15 ft room is 180 sq ft.
How many square feet are in an acre?
43,560 square feet. A quarter acre is 10,890 sq ft.
How do I convert square feet to square yards?
Divide by 9. For example, 450 sq ft ÷ 9 = 50 square yards.
Last reviewed 2026-11-14. Material weights are typical industry averages and vary by supplier, moisture and compaction.