Given a circle with a diameter of 4, the circumference is: 12.6 (diameter x Pi = circumference).
If you only have a given diameter you have to multiply the diameter by Pi (3.142) or 3.14 and then you get the circumference!
It is: pi*diameter
Diameter of a circle = circumference/pi
Diameter = circumference divided by pi. (3.14159)
Divide the circumference by pi (3.141592......) to get the diameter.
Circumference = diameter*pi
If you mean the diameter and radius of a circle given the circumference it is:- diameter = circumference/pi radius = circumference/(2*pi)
Circumference of a circle = diameter*pi Diameter of a circle = circumference/pi
Diameter = circumference/pi Radius = circumference/2*pi
Given the diameter of the circle, multiply it by π (approx 3.14159).
The diameter of the circle equals the circumference divided by Pi (3.14159....).