What size is this pillow?
There are multiple sizes in the specs, but only one option to buy with no size listed?
Sorry about that. This is 18x18.
Thanks TT! Now I just need to figure out how many I want to
buy 
what does it mean when it says: “after stuffing the size will decrease”?
are these not already stuffed or just a shell or we get both & have to do the stuffing ourself?
To be honest, we’re not sure either. The pillow insert comes stuffed and you put it inside a decorative case.
Best we can figure is that some of the filling condenses as you’re squishing it in the pillow case.