I'm sure we've all seen the diagrams of various layers of element fusion from hydrogen to silicon in a star that's just about to go supernova.
(Picture from courses.lumenlearning.com)
I suspect these pictures grossly exaggerate the relative radii at which these fusing layers occur for the sake of readability. What would a more accurate to-scale picture of these fusing layers look like?
Now, I assume the answer will vary significantly based on the mass of the star, and I suspect in certain mass regimes some layers will not be fusing at all. I can think of a few other variables that may affect the answer too.
So in CYA fashion, I'll leave it up to the answerer to identify specific illustrative or interesting cases, as I'm not after a specific answer but rather a general feel for how large some of the layers are in comparison to the others.