Use our simple circle calculator to get any of the radius, diameter, circumference and area of a circle by entering one value in the form below.
How to use:
- Type a value in any one field (radius, diameter, circumference, or area)
- The other three values will be calculated automatically as you type
- Clear a field to start with a different value
- Units are not displayed, remember that if the radius, the diameter or the circumference are in unit u, the area will be in unit u2
Circle formulas
Diameter and radius of a circle
The diameter d of a circle with respect to its radius r is d = 2r
Circumference of a circle
The circumference C of a circle can be calcuted from its radius r or its diameter d as C = 2πr = πd
Area of a circle
The area A of a circle can be calculated from its radius r or its diameter d as A = πr² = πd²/4