Circle Square Footage Calculator
Enter your measurements below to get the area of a circle in square feet, square metres, square yards and acres. The live preview draws the circle to scale as you type, labelled on a measured grid, and you can drag its handles to change the measurements.
Area = π × (Diameter ÷ 2)²
Live scale preview
The shape is drawn to scale and relabelled as you type.
An example to start from. Drag a handle or type a measurement and it becomes yours.
Worked example
A circle with diameter 20 ft works out at 314.16 square feet.
| Unit | Area |
|---|---|
| sq ft | 314.16 |
| m² | 29.19 |
| sq yd | 34.91 |
| sq in | 45,239 |
| acres | 0.007212 |
When to use the circle calculator
Round patios, above-ground pools, fire pits, circular garden beds, silo floors and trampolines are all measured this way. The formula is π × radius², and because the radius is half the diameter, a 16 ft round patio works out at 3.14159 × 8 × 8 = 201.06 square feet.
For the formula in full — a diameter-to-square-feet table, plus semicircles and sectors — see the guide to calculating the square footage of a circle.
Measure the diameter, not the radius
Finding the exact centre of a circle on the ground is fiddly and a small error there is doubled in the answer, so this calculator asks for the diameter instead. Stretch the tape across the circle and slide one end along the edge; the longest reading you can find is the diameter, and every other chord will be shorter.
Take the measurement twice, at roughly right angles. If the two readings differ by more than an inch or two, the shape is an oval rather than a circle. An oval’s area is π × half the long axis × half the short axis, which you can approximate here by averaging the two diameters — the error is small when the difference is under about 10%.
Ordering material for a round area
Circles waste more material than rectangles do, because every tile, paver or plank around the edge has to be cut on a curve and the offcut is unusable. Where 10% is a normal allowance for a rectangular tile job, 15% to 20% is safer around a circle.
For a shape that is round at one end and straight at the other — a kidney-shaped pool, a curved patio — measure the straight part with the rectangle calculator, the curved end with the sector calculator, and add the two together.
Frequently asked questions
How do I calculate the square footage of a circle?
Area is π times the radius squared, where the radius is half the diameter. A round patio 16 ft across has a radius of 8 ft, so its area is 3.14159 × 8 × 8 = 201.06 square feet. Measuring the diameter is far easier than finding the exact centre, which is why this calculator asks for the diameter and halves it for you.
How do I measure the diameter of a round patio or pool accurately?
Stretch the tape across the circle and slide one end along the edge until you find the longest reading — that is the diameter, and every other chord you measure will be shorter. Take it twice at right angles; if the two readings differ by more than an inch or two, the shape is an oval rather than a circle, and its area is π × half the long axis × half the short axis.
How much material do I need for a circular area?
Work out the area as normal, then add the waste factor for the material. Circles waste more than rectangles do, because every tile, paver or plank at the edge has to be cut on a curve and the offcut is unusable. Where 10% is normal for a rectangular tile job, 15% to 20% is a safer allowance around a circle.
Other shapes
A space that is not a circle can nearly always be split into two or three of these and added together.
- L-Shaped Room calculator
- Parallelogram calculator
- Rectangle calculator
- Circle Sector calculator
- Square calculator
- Trapezoid calculator
- Triangle calculator
- Triangle (Three Sides) calculator
To add several spaces into one figure, use the multi-room square footage calculator. To turn this area into an order quantity, see the material calculators.
New to the math? The square footage formula for every shape explains the calculation behind each of these tools.