Area of a Circle Calculator
Find the area inside a circle from whichever measurement is easiest to take: the radius, the diameter across, or the circumference around. The answer comes in square inches, square feet, square meters or any other area unit.
- Radius
- 5 in
- Diameter
- 10 in
- Circumference
- 31.4159 in
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Your recent calculations
Results you calculate here are kept on this device so you can come back to them.
Formula
How to use it
- Choose radius, diameter or circumference.
- Enter the value and its unit.
- Read the area, and switch its unit if you need square feet rather than square inches.
Worked examples
A 12-inch diameter: 113.10 in², which is 0.07297 m²
- Area
- 113.0973 in²
- Circumference
- 37.6991 in
A circle with a 3 m radius
- Area
- 28.2743 m²
A circle 10 m around
- Area
- 7.9577 m²
Radius or diameter?
The formula uses the radius, which is half the width of the circle. Plugging the full diameter into πr² is the classic error and gives an answer four times too big. If you measured straight across, choose “Diameter” and the halving is done for you.
Comparing round sizes
Area grows with the square of the width. A 12-inch pizza is 113 in², a 14-inch is 154 in², and a 16-inch is 201 in² — so the 16-inch gives 78% more pizza than the 12-inch.
Questions people ask
What is the area of a circle with a 12-inch diameter?
The radius is 6 inches, so the area is π × 6² = 113.10 square inches.
What is the area of a circle with a radius of 5?
π × 25 = 78.54 square units.
How do I find the area from the circumference?
Square the circumference and divide by 4π. A circle 10 m around has an area of 100 ÷ 12.566 = 7.96 m².