math
Circle Calculator
Calculate the area and circumference of a circle from its radius, with a labeled diagram.
Area (square units)
78.54
Circumference (units)
31.42
Diagram
How it works
- 1Enter the circle’s radius.
- 2Read the area (π × r²) and circumference (2 × π × r).
- 3Check the labeled diagram for the radius line.
Use cases
- Size a circular table, rug, or garden bed.
- Find the circumference for edging or trim.
- Check homework on circle area and circumference.
Frequently asked questions
What is the formula for the area of a circle?
Area = π × radius². With a radius of 5, the area is about 78.54 square units.
What is circumference?
The distance around the circle, equal to 2 × π × radius. With a radius of 5 it is about 31.42 units.
Can I enter the diameter instead?
Enter the radius, which is half the diameter. For a 10-unit diameter, enter 5.
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