The diameter of the small circle is 2, the diameter of the second circle is 3, and the diameter of the third circle is 4, so the diameter of the big circle is 9 and the radius is 4.5. Formula: perimeter c = 2 π r = π d, where r is the radius and d is the diameter perimeter c = 2 * 3.14 * 4.5 = 3.1.