The Radius (r) is the distance from the center outwards.
The Diameter (D) goes straight across the circle, through the center.
The Circumference (C) is the distance once around the circle.

Circumference (C) of a circle = 2 * π * r = π * D (As D = 2 * r)

Let there be a with Centre as O
Radius = r = 16
Thus Diameter = D = 2 * 16
Thus Diameter = D = 32
Here π = 22/7 = 3.1415926535898
Circumference of a Circle = 2 * π * r
Circumference of a Circle = 2 * π * 16
Circumference of a Circle = 32 π
Circumference of a Circle = 2 * 3.1415926535898 * 16
Thus perimeter of a Circle = 100.53096491487