S: fit for the Pet: the Bust size below 11.8-inch/ 30cm, max weight up to 5.5lbs/ 2.5kg, the distance of the front and back legs less than 3.5-inch/ 9cm. M: fit for the Pet: the Bust size between from 9.8-inch to 15.6-inch(25cm to 40cm), max weight up to 7.7lbs/ 3.5kg, the distance of the front and back legs less than 3.9-inch/ 10cm. L: fit for the Pet: the Bust size between from 13.3-inch to 15.7-inch(34cm to 48cm), max weight up to 12.1lbs/ 5.5kg, the distance of the front and back legs less than 4.3-inch/ 11cm. Notice: the Canvas carrier hasn’t Elastic, so we suggest you to chioce the bag’s size bigger 3-4cm than the recommended Bust size. For example, if your pet’s bust size is 28cm, avoid to any unfit, we suggest you choice the M, not S ones. Air ventilation windows on the front side. Front pack design easier for you to take care of your pet.You also can take it as backpack. Head out design, to hold the whole pet and let your pet enjoy a soothing stroll while keeping your hands free. Magic pad and zipper on the two sides protect your pets from flopping. Widen Shoulder Strap, more comfortable. Material: made of high quality Canvas, fully washable. Package include 1pcs/set Carrier(pets not included).