Dogs in Play Multi-Function LED Lighted Dog Collars - Large 16&rdquo;-20&rdquo; long, 1" wide Large collars: 16-20 long, 1" wide 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. Three different light settings allow you to choose based on your activity - Steady On (non-flashing), Slow Flashing, Quick Flashing Light strip wraps around the full length of the collar