○ Circle Calculator
Area, circumference and diameter from any value
About this calculator
Everything you can know about a circle from a single measurement. Enter the radius, diameter, circumference, or area, and the calculator derives the rest using the standard formulas: C = 2πr, A = πr², d = 2r. It can also compute the area of a sector when you give a central angle — handy for pizza-slice math, pie charts, and sprinkler coverage.
Tip: if you only know the circumference (like measuring around a tree trunk), divide by 2π to get the radius before computing anything else.