Circle calculator
Know one measurement of a circle? Get the other three, and the arc and sector for any angle.
Questions people ask
What are the circle formulas?
Diameter d = 2r, circumference C = 2πr = πd, area A = πr². An arc of angle θ degrees has length 2πr × θ ÷ 360 and its sector has area πr² × θ ÷ 360.
How do I find the radius from the area?
Divide the area by π and take the square root: r = √(A ÷ π). An area of 100 gives a radius of about 5.642.