With the help of a flexible measuring tape measure the dog’s body. For achieving near-to-perfect measuring accuracy, make your dog stand squarely. Start measuring from a point about 2 inches behind the front legs. The Perfect Fit system has three size ranges with just about sized clips and buckles for each. Start with the measurement of the dog’s girth. Ascertain the girth piece size and perfect fit size range. Then find the right front and top pieces. Put together the three pieces (girth strap, front, and top pieces) and put the harness on the dog.