How to find the center of a face on a cylinder

[babyorca3000 (aroishere)]

I’m posting this for a friend since he cannot post himself

So basically I’m trying to model a cannon and am trying to size down a part to another with a wedge in between as a slope.

So in order to properly make the slope between the two parts I need to know the size of one of the faces of the cylinders to make the wedges the same size.

so is there any way to find it with a plugin or something?

(I don’t use blender nor do I know how to script.)

[grimmerschool2 (notGrim)]

Since GapFill is supported on unions, you can fill a face using it and then find the center.