IMPORTANT SIZING NOTE: Different sellers have different size charts standard. Your dog usually wears size "M" doesn't mean all size "M" will fit him/her. If your dog is between sizes, please size up. If there is a difference between the neck and the chest, follow the chest size. If your dog is underage, please take the growth factor into consideration when choosing the size. Leave room for at least two fingers to make the dog feel comfortable and not choke.