⭕ Circle Calculator
Calculate area, circumference, diameter, and radius of a circle. Enter any one value.
Enter Any One Value
Radius
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Diameter
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Circumference
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Area
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Arc Length (90°)
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Sector Area (90°)
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Circle Formulas
Radius: r
Diameter: d = 2r
Circumference: C = 2πr = πd
Area: A = πr²
Arc Length: L = (θ/360°) × 2πr
Sector Area: A = (θ/360°) × πr²
Diameter: d = 2r
Circumference: C = 2πr = πd
Area: A = πr²
Arc Length: L = (θ/360°) × 2πr
Sector Area: A = (θ/360°) × πr²
Circle Theorems
- The angle in a semicircle is always 90°
- The angle at the centre is twice the angle at the circumference
- Angles in the same segment are equal
- Opposite angles in a cyclic quadrilateral sum to 180°