How to Choose a Dog's Cage

There is a saying that we should choose a cage that is three times the size of a dog, but how can we calculate it to be three times the size? If calculated from volume, the top and corners of the cage are actually unusable spaces for dogs. Some people say that just enough width for the dog to turn around is enough. I personally think it is relatively simple to choose the size of the cage, which is twice the length of the dog's body. It should be more suitable for the dog. But if the dog you buy is a puppy, you should consider its growth, so the cage must be purchased according to the adult size of the dog.