Essentially, the size of the coat refers to the length of your dogs back. Measure from the base of the neck to the beginning of the tail. It's important that your dog is standing up, they get longer when they lay down. If your dog is between sizes move up or down based on whether they are broad chested or narrow... Big shouldered Boxers (for example) usually move up a size while slender dogs often op for a smaller size. We've included some weigh suggestions below, but we highly recommend measuring your dog as well.