How it works
Area = π × radius²circumference = 2 × π × radius · π ≈ 3.14159
- radius
- from the centre to the edge
- π
- pi, about 3.14159
- Area
- the space inside, in square units
Use the radius, not the diameter. The diameter is the full width across the centre, so it is twice the radius.
Frequently asked questions
What is the area of a circle with radius 5?
About 78.54 square units, from π × 5².
How do I find the area from the diameter?
Halve the diameter to get the radius, then use π × radius². A 10-unit diameter gives an area of about 78.54.
What is the formula for the area of a circle?
Area equals pi times the radius squared, π r².
What is the area of a 12-inch circle?
If 12 inches is the diameter, the radius is 6 and the area is about 113.1 square inches.