According to the USDA, not that much! Click on the link below to use the calculator that they use to determine how large a dog’s cage must be. Measure your dog in inches (not including the tail!), add 6 inches for extra room (how generous of them), then multiply that number by itself. That’s how many square inches a cage must be. For example, if a dog is 18 inches long, not including its tail, the cage only has to be 2 ft. x 2 ft. Most dogs cannot even stand up and wag their tail without touching both sides of the cage at once.