How precise is the value of π used?

The calculator uses JavaScript's built-in Math.PI, accurate to about 15 significant digits, far more precise than the common 3.14159 approximation used by hand.

Can I enter the diameter instead of the radius?

The input field expects the radius; if you only know the diameter, divide it by 2 first, since diameter = 2 × radius.

Circle Calculator

Calculate a circle's area, circumference and diameter from its radius.

How this is calculated

Area = πr². Circumference = 2πr

Assumptions used in this calculation

Precision of π: Uses the built-in floating-point value of π (about 15 significant digits), more precise than the 3.14 or 3.14159 approximations used in manual calculations.

About this calculator

Calculates a circle's area, circumference and diameter from its radius.

Worked example

Radius 5

Result: Area ≈ 78.54, circumference ≈ 31.42

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Frequently asked questions

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Circle Calculator

About this calculator

Frequently asked questions

How precise is the value of π used?

Can I enter the diameter instead of the radius?

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