Sorry I don't use hoops at all when I do my cross stitching

If you are talking about using a hoop while you are doing your cross stitching I don't feel there is any specific size that you have to use. Just use a size that is comfortable for your hands to hold and not too large for the fabric. No matter what size project I am doing I use a 5" plastic hoop. This particular style I can't find anymore. It is a plastic outer ring with a middle metal ring that you squeeze together. I have several but all are only 5" in diameter because this is what is comfortable for me to handle even on very large pieces of fabric. Hope this helps a little.