dogIDS Personalized Reflective ScruffTag Dog Collars WATERPROOF, SMELL-RESISTANT AND REFLECTIVE STRAP BUILT-IN LASER ENGRAVED NAMEPLATE GUARANTEED FOR LIFE FOR MEDIUM-LARGE DOGS: Recommended for dogs 40lbs and up. SIZED TO YOUR DOG'S NECK: Please read sizing information below to determine best size. Wrap a sewing tape or string around your pets neck and measure. You should leave enough room to comfortably slip one finger between the string and your dogs neck so the collar wont be too tight. The length you come up with will be the size of collar you want to purchase. The collar can be adjusted up and down 2 inches from the given length.