Step 1: Stand your dog upright on all four legs (called a "stacked" position)
Step 2: COLLARS: Using a soft rule measure the circumference of the neck where a collar would rest. Add 1-1/2" to 2" (less for tiny dogs).
Step 3: HARNESSES: Use a soft ruler and measure the girth around the widest part directly behind the front legs.
Step 4: CLOTHING: Measure girth as above, plus the "top line" (length) from the collar to the base of the tail.
Step 5: BELLY BANDS: Measure the circumference directly in front of the rear legs.