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Circle CalculatorCalculate Area, Circumference, Diameter • Precise π Calculations • Geometry Tool
Circle Calculations
Area & Circumference
Diameter & Radius
Precise π
Quick Example Circles:
Geometry mathematics
Radius is the distance from the center to any point on the circle
Circle Geometry Complete Guide
Circle Properties
Constant π: Ratio of circumference to diameter, approximately 3.14159
Symmetry: Infinitely many lines of symmetry through center
Center Point: All points equidistant from center (radius)
Perfect Shape: Maximum area for given perimeter (isoperimetric inequality)
Key Formulas
Area: A = πr² = (πD²)/4
Circumference: C = 2πr = πD
Diameter: D = 2r = C/π
Radius: r = D/2 = C/(2π) = √(A/π)
Common Circle Measurements
Unit Circler=1, A=π, C=2π
Standard Pizzar=6", A≈113.1 in²
Car Tirer=13", C≈81.68"
Earth (approx)r=3963 mi, C≈24901 mi