Circle Calculator
Calculate all circle properties including area, circumference, radius, and diameter with step-by-step solutions
Circle Calculator
Enter value in linear units
Circle Formulas & Diagram
Circle Diagram
Basic Formulas
Diameter
d = 2r
Circumference
C = 2πr = πd
Area
A = πr²
Inverse Formulas
r = d ÷ 2
r = C ÷ (2π)
r = √(A ÷ π)
Key Constants
π ≈ 3.14159
2π ≈ 6.28318
π² ≈ 9.86960
√π ≈ 1.77245
Frequently Asked Questions
The diameter is always twice the radius: d = 2r. The radius is the distance from the center to the edge, while the diameter is the distance across the circle through the center. If you know one, you can easily find the other.
Tips
- Enter the dimensions in the same unit for consistency.
- Results update automatically as you type.
- Use the unit selector to convert between different measurement systems.