I have 1/16"thick circles I want to layer to form a sphere. How mush do I have to shorten each circle? The radius is 12"

Not sure we can answer that. Depends on the diameter and, the sides of each circle would have to be tapered. Why not buy a foam sphere at a craft store?

I would draw a Circle actual scale, then Lines through it every 1/16", Figure how you want to attach, at the corners? or a little overlap to increase strength?
Good Luck

THere is no one simple answer to this. (that I am aware of)

Try it on paper, viewing them from the side.. where they appear to be rectangles... lay it out on paper and you can determine what you are looking for.

Or draw a circle and "slice it" in 1/16" slices as mentioned.