Circle Calculator
Enter a radius below to instantly get area, circumference, and diameter.
Area
78.5398
Circumference
31.4159
Diameter
10
Circle Formulas
Area = π × r². Circumference = 2 × π × r. Diameter = 2 × r.
Worked example
A circle with radius 5.
Area: π × 5² = π × 25 ≈ 78.54
Circumference: 2 × π × 5 ≈ 31.42
Frequently Asked Questions
How do you find the area of a circle?
Area = π × r², where r is the radius. Multiply the radius by itself, then by π (about 3.14159).
How do you find the circumference of a circle?
Circumference = 2 × π × r, or equivalently π × d, where d is the diameter.
What's the difference between radius and diameter?
The radius is the distance from the center to the edge. The diameter is the full distance across the circle through the center — exactly twice the radius.
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