The size of the crate depends on what you are using it for. If it is for potty training then a small one will do. You have to be right there to take the pup out often. Puppies potty often and if you want to teach it not to potty in the crate then you have to be near by at all times to take the pup out when needed.   
If the crate is just for travel then enough room is needed to stand and turn around. Considering the size of the pup at maturity will save you from having to get another one later on.   
If you need a crate to leave your pup in while you are gone for several hours then you need one large enough for a bed, dishes, and a potty area. Many people here use that type of crate or playpen and it is a very humane way of keeping your puppy out of trouble when you can't watch it.     |