For Standard Buckle Collars and Thin BioThane Snap Collars:
Measure your dog's neck at the green line #3. Our buckle collars are measured to the middle hole on the collar so you have 1 to 2 inches on either side depending upon the overall collar size. If your puppy is still growing order a size up (if your dog measures at 16" order an 18"), it will fit now on the smallest hole and give the most room for growth.
For Martingales, Slip Collars, Limited Slip Collars, Lola Secret Powers, Prong Collars, and Show Chains:
For a Non-Adjustable Martingale (no buckle), Slip Collar, Limited Slip Collar or Show Chain, order the size at red line #1. For an Adjustable Martingale (with a buckle), Lola Secret Powers, and Prong Collars order the size at blue line #2.
For Show Leads:
Consider the height of your dog, the distance between your waist (where your hand would normally be held) and your dog's neck, as well as the way your breed shows. Does your dog run ahead of you? Then you'll need a longer lead. Does your breed stay by your side on the "go around"? Then you want a length close to the distance between your waist height and the dog's neck height so you don't have as much extra lead to roll in your hand. Does your breed typically wrap the lead over your shoulders when stacking? Then you need a longer lead. A few "typicals":
Sporting breeds typically go with a 36" lead
GSDs are typically 48" or 72"
Toy breeds are usually a 48"
Tall breeds such as Great Danes and Irish Wolf Hounds typically go with a 24"
These are all just recommendations. Everyone has their own preference and your comfort is the most important!