Math

Circle Equation Calculator

Convert between standard and general circle equations, complete the square, and find center, radius, diameter, circumference, and area with steps.

Standard ↔ General Complete the Square Center + Radius Steps + History

Circle Equation Converter

Choose the form you have, enter values, and calculate. The tool converts forms, finds center/radius, and shows key circle measures.

Center h (x-coordinate)

Center k (y-coordinate)

Radius r

Display Precision

Number Formatting

Standard Form Preview

Enter h, k, and r, then press Calculate to expand into general form and compute circle properties.

Tip: A radius must be non-negative. If r = 0, the “circle” is a single point at the center.

D (x coefficient)

E (y coefficient)

F (constant term)

Display Precision

Number Formatting

General Form Preview

Enter D, E, and F for x² + y² + Dx + Ey + F = 0, then calculate to complete the square and convert to standard form.

Tip: If r² turns out negative, the equation does not represent a real circle (no real radius).

Your history will appear here after you run a few conversions.