There is not enough information to answer the question.
If the circumference or diameter is given then you can find the radius or simply measure the distance from the centre of the circle to the circumference.
I guess you mean:"How do you find the radius if you are given the diameter?"You take the diameter and divide it by 2.
A spherical surface, with its center at the given point, and its radius equal to the given distance.
The radius is half the diameter.
Double the radius
the radius is half the diameter
Divide the circumference by 2PI to find the radius. ( C = 2PI*Radius)
They form the sphere whose center is the given point and whose radius is the given distance.
You times the radius by 2.
Circumference = 2*pi*radius