It all depends on your shape. It’s not just about one magic girth number. I’ve mentioned this before, but since I have a thick base I have to wear Magnums. My mid-shaft girth is average. If I wear a normal condom, it can’t roll all the way down the base and so it is MORE likely to slip off than a Magnum. Might seem weird, but each person is different and you should just try them on.