About the Circle Calculator
Solve for radius, diameter, circumference, and area from any one known value, plus arc length and sector area.
What it is
Enter any single circle measurement — radius, diameter, circumference, or area — and the calculator reverse-solves for radius when needed, then derives the other three values, shown as exact π-expressions and decimals.
Features
Solve from any value
Radius, diameter, circumference, or area — enter one, get all four.
Arc & sector mode
Radius and central angle give arc length, sector area, and chord length.
Exact π display
Results shown as exact π-expressions alongside decimals.
To-scale diagram
The circle or sector is drawn to scale with labels.
Formulas used
C = 2πr, A = πr², reverse-solved as r = C/(2π) or r = √(A/π) when starting from circumference or area. Arc/sector mode uses arc length = rθ, sector area = ½r²θ, and chord = 2r·sin(θ/2) with θ in radians.