Dogs in Play Multi-Function LED Lighted Dog Collar - Large Collar (16-20" L, 1" W) Large Collar (16-20" L, 1" W) Correct Collar Size: The sizes listed above indicate the maximum size with the buckle fastened. Measure your pet's neck before ordering. You may wish to add 1" - 2" to the measurement for your dog's comfort. Don't forget to buy a matching leash!