Use the following tips as a guide.
When measuring, try to have your dog stand in a relaxed stance. Use soft tape measure, and measure completely each body part (neck - chest – back/length) Keep the measuring tape slightly loose.
Back: Measure from the base of the neck to the base of the tail.
Neck: Measure all the way around the neck at top of the shoulders.
Chest: Measure all the way around broadest/barrel part of chest or ribcage.