Enter any one value — radius, diameter, circumference, or area — to compute the rest
This circle calculator computes the radius, diameter, circumference, and area of a circle from any single known value. It is useful for geometry problems, construction, crafting, and any application involving circular shapes.
The radius is the distance from the center of a circle to any point on its edge. The diameter is twice the radius — it is the distance across the circle through its center. Diameter = 2 × radius.
Pi (≈ 3.14159) is the ratio of a circle's circumference to its diameter. It is a universal constant that appears in all circle and sphere geometry formulas because it defines the relationship between a circle's linear and curved measurements.