About this circle calculator
All four measurements of a circle follow from one: d = 2r, C = 2πr, A = πr². Enter whichever you have, from a tape measure around a trunk (circumference) to a known area.
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Circle Calculator
Details
How to use Circle Calculator
What the tool does, how to run it, and what to expect from the result.
At a glance
Who Circle Calculator is for
A quick way to understand who this helps, what it solves, and where it connects next.
Best fit
Students, teachers and anyone checking a calculation.
Ideal for
Using the circle calculator without installing anything or signing up.
FAQ
Common questions
Short answers for the questions people usually have before trying a utility like this.
How do I get the diameter from the circumference?
d = C ÷ π. A tree 100 cm around is about 31.8 cm across.
How is the area of a circle calculated?
A = πr². A radius of 5 gives 25π ≈ 78.54.
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