Spike Lighted Dog Collar - Silver - Small/Medium Small/Medium collars adjust from 12-19" (not meant for dogs under 10 pounds), 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