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Circle Calculator
Circle radius, diameter, circumference, area
How It Works
A circle is a simple closed shape: the set of all points in a plane equidistant from a given center point. Given any one of radius, diameter, circumference, or area, the remaining three can be calculated.
A circle is a simple closed shape: the set of all points in a plane equidistant from a given center point. Key parts include the center (origin), radius (distance from center to any point), diameter (largest distance between two points passing through the center), circumference (distance around the circle), and area (space inside the circle).
The constant π (pi) is the ratio of a circle's circumference to its diameter, approximately 3.14159. π is an irrational and transcendental number, meaning it cannot be expressed exactly as a fraction and its decimal never repeats. The three key formulas relate radius (R), diameter (D), circumference (C), and area (A): D = 2R, C = 2πR, A = πR².
Results
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Quick Tips
- • Results update automatically as you type
- • Use Tab to navigate between fields
- • Press Enter to calculate