The formula for circumference is C=2pi(r) so Basically if the circumference was 20 you would set up the equation like so 20=2pi(r) then you simply divide 2pi to both sides and your radius would be 3.18. Hope this helps!
Diameter = Circumference/pi
diameter = circumference/pi
To find the circumference of a circle when you know the diameter, you can use the formula (C = \pi \times d), where (C) is the circumference and (d) is the diameter. Since (\pi) is approximately 3.14, you can multiply the diameter by this value to get the circumference. For more precision, you can use the value of (\pi) to more decimal places, such as 3.14159.
You cannot find the diameter of something from its circumference unless it is a circle and, in that case, diameter = circumference/pi
Circumference = Pi * diameter
Divide the circumference by Pi to find the diameter.
Circumference = diameter(pi) so divide the circumference by pi to get the diameter.
Diameter = radius * 2 Circumference = pi * diameter.
circumference/pi = diameter
diameter*pi = circumference
Diameter = circumference/pi
Circumference: Diameter x pi (3.1415926535897932384...)