Circle Calculator
Calculate circle area, circumference, diameter, and radius with visual representation
Circle Calculator
Choose what you know about the circle and enter the value
Visual Representation
Radius (r)
Diameter (d)
Circumference
Linear Measurements
Radius:
5 units
Diameter:
10 units
Circumference:
31.415927 units
Area Measurements
Area:
78.539816 sq units
Alternative Units:
Area (π × r²):25π sq units
Area (exact):π × 5²
Circle Formulas
Basic Relationships
Radius to Diameter:
d = 2r
Circumference:
C = 2πr = πd
Area:
A = πr²
Reverse Calculations
Radius from Circumference:
r = C / (2π)
Radius from Area:
r = √(A / π)
π (Pi) ≈ 3.14159
Ratio of circumference to diameter
Common Circle Examples
Unit Circle
Radius: 1 unit
Diameter: 2 units
Circumference: 2π ≈ 6.28 units
Area: π ≈ 3.14 sq units
Pizza (12 inch)
Diameter: 12 inches
Radius: 6 inches
Circumference: 37.7 inches
Area: 113.1 sq inches
Wheel (50cm radius)
Radius: 50 cm
Diameter: 100 cm
Circumference: 314.2 cm
Area: 7,854 sq cm
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