Solve key circle measurements from any known circle dimension.
Circle geometry links several measurements through pi, making it possible to compute unknown values from a single known value. This is useful in machining, architecture, and classroom geometry.
Radius and diameter control every other circle property. Once either is known, circumference and area follow directly. Confusing these measures is a common source of error when planning circular parts.
This calculator helps move between circle dimensions quickly while preserving unit consistency. You can use exact pi forms for theory work and decimal approximations for practical measurements.
Pick radius, diameter, circumference, or area as your input.
Type the known value with consistent units.
The tool derives all remaining circle dimensions.
Use pi form for algebra and decimal form for field work.
Check whether output meets tolerance or design constraints.
d = 2r; C = 2pi r = pi d; A = pi r^2
Diameter doubles radius. Circumference scales linearly with radius, while area scales with radius squared because it covers a 2D region.
d=10, C=10pi, A=25pi
Diameter 10 cm, circumference about 31.42 cm, area about 78.54 cm^2.
r=6, C=12pi, A=36pi
Circumference about 37.70 m and area about 113.10 m^2.
r = C / (2pi) = 50/(2pi)
Radius about 7.96 ft and area about 199.0 ft^2.