How to calculate square footage
Square footage is the area of a flat surface measured in square feet. Measure in feet, then use the formula for the shape:
Rectangle or square: length × width
Circle: π × radius × radius (radius = diameter ÷ 2)
Triangle: base × height ÷ 2
If you measured in inches, divide the square inches by 144 to get square feet (or divide each measurement by 12 first). To convert the result, divide square feet by 9 for square yards, by 43,560 for acres, or by 10.764 for square meters.
Most real yards are not perfect rectangles. Split an L-shaped or irregular area into simple shapes, calculate each one with the calculator above, and add the results together. For a cut-out, such as a shed or a flower bed you will not cover, subtract its area.
Worked example: an L-shaped backyard
Say a backyard is made of a 30 ft by 20 ft main lawn plus a 10 ft by 12 ft strip along the side.
- Main lawn: 30 × 20 = 600 sq ft
- Side strip: 10 × 12 = 120 sq ft
- Total: 600 + 120 = 720 sq ft
- In square yards: 720 ÷ 9 = 80 sq yd
- In acres: 720 ÷ 43,560 = 0.0165 acres
- In square meters: 720 ÷ 10.764 = 66.9 m²
At a price of $0.50 per square foot, covering it would cost about $360. Once you have the area, the next step depends on the job: the sod calculator turns it into rolls and pallets, and the grass seed calculator into pounds of seed.
Area conversions at a glance
| Unit | In square feet | From square feet |
|---|---|---|
| 1 square inch | 0.00694 sq ft | sq ft × 144 |
| 1 square yard | 9 sq ft | sq ft ÷ 9 |
| 1 square meter | 10.764 sq ft | sq ft ÷ 10.764 |
| 1 acre | 43,560 sq ft | sq ft ÷ 43,560 |
| Size | Square feet | Square yards |
|---|---|---|
| 10 × 10 ft | 100 | 11.1 |
| 12 × 14 ft | 168 | 18.7 |
| 20 × 20 ft | 400 | 44.4 |
| 50 × 100 ft | 5,000 | 555.6 |
| Circle, 20 ft across | 314.2 | 34.9 |
From square feet to materials
Area is the starting point for almost every yard project. Materials spread in a layer, such as mulch, topsoil, gravel or sand, also need a depth to become a volume, so they have their own calculators: the mulch calculator, the topsoil calculator, the gravel calculator and the sand calculator. For hardscaping, use the paver calculator or the concrete calculator.
Frequently asked questions
How do I calculate square footage?
For a rectangle, multiply the length by the width, both in feet. For a circle, multiply π by the radius squared; for a triangle, multiply the base by the height and divide by 2. Split irregular areas into these shapes and add them up.
How many square feet are in an acre?
One acre is 43,560 square feet. Divide a square footage by 43,560 to convert it to acres; a 5,000 sq ft lot is about 0.115 acres.
How do I convert square feet to square yards?
Divide by 9, because a square yard is 3 ft by 3 ft. For example, 720 sq ft equals 80 square yards.
How do I find the square footage of a circle?
Measure the diameter, halve it to get the radius, then multiply π (about 3.1416) by the radius squared. A circle 20 ft across has an area of about 314.2 sq ft.
How do I measure an irregular yard?
Sketch the yard and divide it into rectangles, triangles and circles. Measure and calculate each part separately, add the areas together, and subtract any parts you will not cover, such as a patio or a shed.
More free calculators
These calculators give estimates for planning only. Densities, bag sizes and coverage vary by supplier, so confirm quantities before you order.