Spike Lighted Dog Collar - Yellow - Medium/Large Medium/Large collars adjust from 16-27" long and are 1.5" wide Correct Collar Size: Measure your dog's exact neck size and add 4" for correct collar size. For dogs with 8", 10", and 12" necks, only add 2". Reflective and pulse with a brilliant light visible from 360 degrees at night Operate up to 300 hours using two AAA batteries