Circle Calculator
Math
Calculate the area and circumference from a radius.
Formula
Area = πr²; circumference = 2πr
- Use the units shown beside each field.
- Results update automatically whenever you change an input.
- Displayed values use up to four decimal places, or scientific notation for very small or large numbers. Calculations retain full precision.
Example Calculation
Example inputs
- Radius: 5 m
A radius of 5 m gives an area of 78.54 m².
Frequently asked questions
How do I use this calculator?
Enter radius. The result updates automatically. Use Reset to restore the example values.
What method does it use?
Area = πr²; circumference = 2πr. Follow the units and definitions shown with the inputs to apply this relationship consistently.
Why might a rounded result differ?
The calculation keeps full numeric precision internally, then rounds the displayed result. Rounding intermediate steps by hand can produce a slightly different answer.
Are my inputs saved online?
No. This calculator processes your inputs in your browser. A recently used list stores only calculator names on this device, not your entered values.
Check the assumptions and units before using this result. Read about calculation methods.