SIZE YOUR PET COLLAR To determine which size collar to order, measure your pet's neck, allowing sufficient leeway for comfort (we suggest adding 2"), and that is the size you order. As a final note, make sure to attach a tag to the collar that has proper identification in case he should get lost. This should include your name and phone number where you can most easily be reached. I do not advise putting the pets name on the tag. Unfortunately there are some people who might want to keep your pet ,and if it comes when called by name the chances of returning the pet to you are far less.....very sad To measure for a HARNESS the area just behind the front legs all the way around the CHEST also known as the GIRTH. I will need the neck size and the girth measurements for a custom harness order. SWEATERS Measure from the back of the neck to the base of the tail. image0