Four basic measurements, plus your dog's weight, helps me develop the fit model. They are
1) Neck circumference (see picture below)
2) Chest circumference (see picture below, as measured about an inch or two behind the elbows of the front legs)
3) Shoulder width (this is best done by sending me a top view picture of a measuring tape draped across the pup's shoulders)
4) Back length, as measured from the base of the neck to the base of the tail.