How to use the Circle Tools
Circle Tools find the radius, diameter, circumference and area of a circle from any one of them.
The formula
Diameter = 2r. Circumference = 2πr. Area = πr².
Worked example
For a radius of 5: diameter 10, circumference 31.416, area 78.54.
Tips for better results
- Enter whichever value you know; the rest are filled in.
- Use the same unit for all measures; area is in square units.
Common mistakes to avoid
- Using the diameter where the radius is needed in the area formula.
- Rounding π too early.