How this calculator works
Each shape has a simple formula. Dimensions in any unit are converted to feet first, so you can mix, for example, inches and meters.
Worked example: a 20 × 15 ft rectangle is 300 ft², which is 33.3 yd², 27.9 m² or 0.0069 acres. A 20 ft diameter circle is π × 10² = 314.2 ft².
Once you have the area, plug it into a materials calculator: choose "I already know the square footage" on the mulch, gravel, flooring or tile calculators.
Tips before you buy
- Break complicated shapes into simple ones. An L-shaped room is two rectangles. A garden bed with a curved side is a rectangle plus a half-circle.
- Measure twice, in the same unit, and write dimensions down as you go.
- One acre is 43,560 ft². A square lot 209 ft on each side is about an acre.
Tools & materials for this project
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Frequently asked questions
How do I calculate square footage?
For a rectangle, multiply length by width, in feet. For other shapes use the formulas above. For irregular areas, split into simple shapes and add them.
How many square feet are in an acre?
43,560 square feet.
How do I convert square feet to square yards?
Divide by 9. A square yard is 3 ft × 3 ft.
Related calculators & guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.