How big is a shih tzu across the shoulders you want to get a dog door for him?

A Shih Tzu typically measures about 9 to 10.5 inches in height at the shoulder and weighs between 9 to 16 pounds. When selecting a dog door, you should consider a width of at least 10-12 inches to ensure comfortable passage. It's also a good idea to account for their body shape, as Shih Tzus can be a bit stocky. Always check the specific measurements of your dog to ensure a proper fit.