How to calculate square footage
Measure the length and the width in feet, then multiply them. The answer is the area in square feet (ft² or sq ft). If a measurement has inches, divide the inches by 12 and add them to the feet first: 12 ft 6 in is 12.5 ft.
The radius is half the distance straight across a circle. The height of a triangle is measured square to the base.
Worked example
An L-shaped patio splits into two rectangles. Rectangle A is 20 × 12 ft, which is 240 square feet. Rectangle B is 10 × 8 ft, which is 80 square feet. Together they make 320 square feet. Divide by 9 for 35.6 square yards, or by 10.764 for 29.7 square metres.
Measuring odd shapes
- Split the space into rectangles first. Most yards, patios and rooms are a few rectangles joined together.
- Treat a round bed or a fire pit area as a circle. Measure straight across the middle to get the diameter.
- For a triangle, measure the height square to the base, from the base to the far corner. Don't measure along the sloping side.
- If something sits inside the area and won't be covered, like a shed or a pool, work out its area on its own and subtract it from the total.
Square footage conversions
| Unit | In square feet | Metric |
|---|---|---|
| 1 square foot | 144 square inches | 0.0929 m² |
| 1 square yard | 9 square feet | 0.8361 m² |
| 1 square metre | 10.764 square feet | 1 m² |
| 1 acre | 43,560 square feet | 4,047 m² |
| 1 hectare | 107,639 square feet | 10,000 m² (2.471 acres) |
From square feet to materials
Gravel, mulch, topsoil and concrete are sold by volume, so you also need a depth. Multiply the square feet by the depth in inches and divide by 324 to get cubic yards.
The 320 square foot patio above, covered 3 inches deep, needs 320 × 3 ÷ 324 = 2.96 cubic yards before any extra. The links under your estimate open the gravel, mulch, topsoil, sand and concrete calculators with your area already filled in. They add compaction, settling and bag counts for each material.
Common questions
How do I calculate square footage?
Measure the length and width in feet and multiply them. A 12 × 15 ft room is 12 × 15 = 180 square feet. Convert any inches to feet first by dividing by 12.
How many square feet are in a square yard?
Nine. A square yard is 3 feet by 3 feet, and 3 × 3 = 9. To turn square feet into square yards, divide by 9.
How many square feet are in an acre?
43,560. A square acre is about 208.7 feet on each side.
How do I find the square footage of an irregular shape?
Split it into rectangles, circles and triangles. Work out each one and add them up. In the calculator, enter the first shape, press "Add another section", then enter the next.
How do I convert square feet to square metres?
Divide by 10.764. To go the other way, multiply square metres by 10.764.
How do I turn square feet into cubic yards?
You need a depth. Multiply the square feet by the depth in inches, then divide by 324. For example, 320 square feet at 3 inches deep is 320 × 3 ÷ 324 = 2.96 cubic yards.
Sources: NIST Guide to the SI, Appendix B.9 (area conversion factors); NIST, the international foot (0.3048 m). More on how we calculate.