Calculate the area, circumference, and diameter of a circle from its radius.
Last updated: June 2026 | By Patchworkr Team
Live results update as you type
Radius needs a real number.
A circle is the set of all points that are the same distance from a fixed center point.
The radius is that distance. From it, we can derive the diameter, circumference, and area.
This calculator keeps the formulas tied to the radius so the outputs stay mathematically consistent.
For a radius of 5, the area is pi * 25, the circumference is 10pi, and the diameter is 10.
The area is roughly 78.54 square units, which matches the standard circle formula.
Can the radius be zero?
No. A radius of zero does not describe a meaningful circle for this calculator.
Does the area always use pi?
Yes. The exact area formula is pi * r^2.
How do I get the diameter?
Multiply the radius by 2. The calculator shows it automatically.
Are the outputs live?
Yes. The result card updates as soon as the radius changes.
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