Circle Calculator
Calculate any circle property from a single known value. Enter the radius, diameter, circumference, or area, and this calculator instantly computes all other measurements.
The circle is one of the most fundamental shapes in geometry. All points on a circle are equidistant from the center, and this distance is called the radius.
Circle Formulas
- Diameter: d = 2r
- Circumference: C = 2 x pi x r = pi x d
- Area: A = pi x r^2
Where r is the radius and pi is approximately 3.14159265358979.
Working Backwards
From circumference: r = C / (2pi). From area: r = sqrt(A / pi). From diameter: r = d / 2. Once you know the radius, all other properties follow directly.
Circles appear everywhere in engineering (wheels, gears, pipes), architecture (domes, arches), nature (planets, bubbles), and mathematics (trigonometry, polar coordinates, complex numbers).