Circle Calculator
Enter the radius, diameter, circumference, or area of a circle. Get the other three values plus the central angle of arc length.
Properties
How to use
- 1
Pick which value you already know.
- 2
Enter that value.
- 3
The other three values are computed instantly.
Frequently asked questions
The radius is the distance from the centre of the circle to its edge. The diameter is the distance across the circle through its centre — twice the radius. So d = 2r.
π (pi) is the constant ratio of a circle's circumference to its diameter — approximately 3.14159. The area of any circle equals π × r². This relationship was known and approximated by ancient civilisations (Babylonians, Egyptians, Indians) long before its irrationality was proven.
JavaScript uses IEEE 754 double-precision floating-point for π and √, which gives roughly 15-17 significant digits of accuracy. For everyday geometry, surveying, engineering drawings — far more than precise enough.
No. Radius is a distance, so it must be non-negative. Negative inputs are rejected.
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Source: Standard circle geometry formulas · Last verified 2026-06. This tool provides estimates only and is not legal, tax or financial advice. Always verify your specific situation with the relevant UAE authority or a licensed advisor before taking action.