Circle Area and Circumference Calculator

Enter a circle’s radius to calculate its area, circumference and diameter.

Circle Area and Circumference Calculator

Calculate the area, circumference and diameter of a circle from its radius.

This is a mathematical calculation. Use the same unit for the radius throughout, and results will be in that same unit (area in square units).

A circle’s area and circumference are both derived from its radius using the constant π (pi). This calculator computes the area (π times radius squared), circumference (2π times radius) and diameter (twice the radius) all at once.

Example

  • With the default values shown above, this calculator returns: Area ≈ 78.540; Circumference ≈ 31.416; Diameter ≈ 10.000.

Frequently Asked Questions

What value of pi does this use?

This calculator uses π ≈ 3.14159265358979, accurate to well beyond typical rounding needs.

Can I enter a diameter instead of a radius?

Divide the diameter by 2 first to get the radius, since this calculator’s formulas are based on radius.

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