Adult size is one of the best clues to figuring out what kind of lop a bunny is, so trying to guess breed to determine adult size is a bit like putting the cart before the horse.
A few clues though. Fuzzy lops, have long fur, all other lops have short fur. Holland lops have arched shaped bodies and short ears and dwarf features. Mini lops are fairly similar to hollands, but are slightly larger, slightly more cylindrical, and have very square heads. French lops are much more cylindrical, have more triangular heads, and longer ears. English lops like french lops have cylindrical bodies, most distinctive is their ears which are like velvet blankets you can wrap up in, the english’s ears are so long they form velvet puddles on the floor.
breed standard weights are: fuzzy lop-up to 4lbs; Holland lop-up to 4lbs; mini lop-up to 6.5 lbs; french lop is a giant breed that can get bigger than a cat; english lops are also a giant breed that gets bigger than a cat.
Of course, it is also possible your rabbit is not a pure breed lop and is a mix of different lop breeds or a lop and a none lop. Also even pure breeds don’t always match breed standard for size. You can end up with a 5lb fuzzy lop and although not a good show rabbit is still a fuzzy lop.