What is a circle calculator?
A circle calculator uses one known circle measurement to derive the others. If you know the radius, diameter, circumference or area, this page calculates the complete set. For root calculations used in area-to-radius conversions, see the Square Root Calculator.
How does the circle calculator work?
The selected input is converted to radius. From that radius, the calculator uses the standard Euclidean relationships d = 2r, C = 2πr and A = πr². This keeps all result fields based on one internally consistent radius.
What formulas does the circle calculator use?
You can evaluate related powers with the Exponent Calculator.
How do you use this circle calculator?
- Select Radius, Diameter, Circumference or Area.
- Enter one positive measurement.
- Choose an optional unit label.
- Select Calculate Circle.
- Review radius, diameter, circumference and area.
Circle calculator examples
A circle with radius 5 has diameter 10, circumference about 31.4159 and area about 78.5398. Starting with diameter 10, circumference 31.4159 or area 78.5398 returns the same radius within display precision. For percentages applied to measurements, use the Percentage Calculator.
How are units handled?
The calculator does not convert between unit systems. If you choose centimeters, radius, diameter and circumference are labeled cm while area is labeled cm². If you select No unit, results are shown as pure numeric values.
What are the calculator's limits?
The known measurement must be a positive finite number. Very large measurements can exceed browser number limits, and irrational results involving π are rounded for readable display.
Frequently asked questions about circles
Methodology and calculation scope
The calculator uses JavaScript's Math.PI and double-precision floating-point arithmetic. All calculations describe a Euclidean circle and run locally in the browser.