if I have a length AB, defined by points A and B, how do I construct a circle with circumference AB with a compass?

Question

I want to construct a circle with a given linear circumference with compass and straightedge. I know that you cant construct a length ¨pi¨ if the linear distance is ¨1¨, but can you find the radius?

I want to do this so I can possibly take the relationships of a square, and its divisibility into n equal parts, and copy it onto a circle, and vice versa

Answer 1

You'd need to construct $\frac1{2\pi}$, which is also impossible.