I always pre-wash my fabric and then check the batting for what it says for shrinkage. Cotton batting can shrink 2-5%. So for a queen size that I want 90" wide all done, I start with 94-96 wide. Then after shrinkage I have the size I want.
Basic math - 90" finished x 5% (90x1.05 = 94.5)
I don't know how you would account for fabric shrinkage if you don't pre-wash, it all shrinks differently and isn't marked like batting is.