(point is not a property of a circle)

(x - x_0)^2 + (y - y_0)^2 = r^2 (assuming center (x_0, y_0) and radius r)

diameter | 2 r area enclosed | π r^2 circumference | 2 π r≈6.28319 r (assuming center (x_0, y_0) and radius r)