The area of a circle is π times the radius squared. Enter the radius to get the area, or switch to “Radius” to work backwards from a known area. Diameter and circumference are shown too. Use any unit — the area comes out in that unit squared.
Formula
A = π × r ^ 2
Where A is the area, r is the radius.
Choose any value to calculate — the calculator rearranges the formula for you.
Worked example
A circle with a radius of 5 cm has an area of π × 5² ≈ 78.54 cm², a diameter of 10 cm and a circumference of about 31.42 cm.
Frequently asked questions
How do I find the area of a circle from the diameter?
Halve the diameter to get the radius, then use A = π × r². A 10 cm diameter gives r = 5 cm and A ≈ 78.54 cm².
How do I find the radius from the area?
r = √(A ÷ π). Choose “Radius” under Calculate and enter the area.
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