According to vets and dog trainers, a dog bag must be large enough for your dog to lie down and turn around comfortably. In addition, your dog should be able to stand in the dog bag without any problems.
If you want to buy the dog bag in a pet shop, we recommend that you take your dog with you when you buy it. This way you can try out on the spot which dog bag is suitable for your pet.
If you buy your dog bag on the internet, you should try it out at home to see if it is suitable for your dog.
If you like to fly with your dog, you must observe the regulations of the respective airline and the IATA. The IATA - International Air Transportation Association - sets international regulations on the size of dog bags, age of the dog, etc.