Unit Converter
Circle Area Calculator
Calculate circle area and circumference from radius.
Formula and usage notes
area = pi x radius squared; circumference = 2 x pi x radius.
Calculate circle area and circumference from radius.
Practical examples
Radius 5 gives area about 78.54 and circumference about 31.42.
Use diameter / 2 when only diameter is known.
Keep pi precision until the final rounded answer.
Frequently asked questions
What inputs does this calculator need?
Radius.
How should I round the result?
Keep extra digits while comparing values, then round for the final decision or report.
Can I reuse the result in another calculation?
Yes, but preserve the original inputs and units so the next calculation stays traceable.