1.) The Broadest part of the chest (shown as Chest on the illustration above) For chest measurement, measure the chest at its widest point, which is typically right behind the front legs. If the dog has a large girth, going up a size in the top line measurement is always a smart choice, since some additional fabric will be used up. 2.) The Length of the backbone (shown as Back Length on the illustration above) Measuring should be done along the dog's backbone from the base of the head to the base of the tail. This is from the base of where the collar rests to where the tail is attached. The measurements you see on all our apparel indicate this top line measurement. However, it's important that the dog's girth be taken into account as well as the top line measurement. 3.) The Circumstances of the neck (shown as Neck on the illustration above) The neck size determine whether the dog will be comfortable wearing clothing. If the neck is too tight, the dog would be hard to breath. There are different sizing ranges for different types of garments, due to how binding or flexible the material used is. The most important is the chest size, so if the chest size is ok the other will not be big matter.