1.measurement for Chest------ the slightly posterior position from Front legs,should choose 2-3cm bigger than you actual measured. The most important thing is that :Size choice would rather to choose big than samll based on the actual size!
2.measurement for back length-----Neck to the tail. But don't close to tail to measure,as the clothes is not need to wear to tail.
3.measurement for neck-----the Circumference of neck, it is better choose 2-3cm bigger than you actual measured.