Circle Calculator
Calculate the circumference, area, diameter, or radius of a circle from any one known measurement.
Inputs
Radius
โ
Diameter
โ
Circumference
โ
Area
โ
About Circle Calculator
Formulas
d = 2r. c = 2ฯr = ฯd. A = ฯrยฒ. Memorize these four and you can derive any circle property from any other.
Pi (ฯ)
The ratio of a circleโs circumference to its diameter. Approximately 3.14159265... โ an irrational number with no exact decimal representation. This calculator uses JavaScriptโs Math.PI (~15 decimal places).
Common uses
Pizza math (compare areas: 10" vs 12" pizza). Bicycle wheel rotations from circumference. Cake pan sizing. Garden bed area. Wire length wrapped around a cylinder.