Circle calculator
Circumference: 18.8496 m
Area = πr²; circumference = 2πr
Formula
Area = πr²; circumference = 2πr
How the calculation works
Calculate circle area and circumference from its radius. Enter each measurement in the unit shown beside the input. The result updates when you change a value; incomplete or unsupported inputs display an explanation.
Worked example
A radius of 3 m gives an area of about 28.2743 m² and circumference of 18.8496 m.
When to use this calculator
Use this for circular surfaces and boundaries.
Common mistakes and limits
Radius is half the diameter. Entering the diameter as the radius quadruples the area.
Check your result
Check that all measurements describe the same object or time period. Repeat the calculation with unrounded values, then round only the final quantity to a precision suitable for the task.
Frequently asked questions
Does this calculator need an account?
No. Calculations run in your browser without an account.
How precise is the displayed result?
The display rounds to six decimal places. Measurement uncertainty can be larger than this rounding.
