What is the ratio of the circumference and diameter of any circle?

The circumference of a circle is calculated using the following formula:

c = 2 π r

where:

c is the circumference

r is the radius

π is the constant of pi (3.14159....)

Since the radius is equal to half of the diameter, this formula can also be written as:

c = π d

Or, alternatively:

d = c / π