How to use Circle Calculator
- Choose which value you know: radius, diameter, circumference or area.
- Enter it.
- Read the other three values.
About this tool
Every property of a circle follows from its radius r: diameter = 2r, circumference = 2 x pi x r and area = pi x r squared. If you know the area or circumference instead, the calculator works backwards to find the radius first.
Results use the full precision of pi and are rounded for display only.
Frequently Asked Questions
- What is the difference between radius and diameter?
- The diameter passes through the center and is twice the radius.
- What units does it use?
- Any consistent unit. Area is in square units of whatever length unit you entered.
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