Circle Calculator
Area and circumference.
Enter your values in the interactive calculator to see an instant result. Calculations run in your browser, without an account.
Results are estimates for educational use; confirm important decisions with appropriate experts.
Formula • Worked example • Interpretation
Circle area, circumference and diameter
A circle’s radius is the distance from its center to the edge. From the radius you can compute its area, circumference and diameter.
Calculation method
Worked example
A circle with radius 3 cm has area ≈ 28.27 cm², circumference ≈ 18.85 cm and diameter 6 cm.
What your result means
Doubling radius doubles circumference but quadruples area because area depends on radius squared.
Tips for better calculations
Check whether your measurement is radius or diameter before entering it; confusing the two produces a fourfold area difference.
Assumptions and limitations
All formulas assume a flat Euclidean circle. The numerical value of π is approximate in floating-point software.
SiCalcs tools provide estimates and educational calculations; they do not replace professional financial, medical, tax, or legal advice.