Excursion back pack is comfortable and convenient for you and your pet Dog pack holds water and treats Pet back pack is perfect for short hikes and walks Sizing Guide: Instructions: Measure length of pet's back from the base of the neck to the base of the tail. Note: If the dog has a stout build, select one size larger. For long body dogs, go down one size to ensure a correct fit in the girth XX-Small fits up to 6 inches X-Small fits 6 - 8 inches Small fits 8 - 12 inches Medium fits 12 - 16 inches Large fits 16 - 20 inches X-Large fits 20 - 24 inches XX-Large fits 24 - 30 inches 100-percent nylon Machine washable Model number 13227