This BEAUTIFUL double row martingale collar is made from 2.5mm high quality chrome chain. Measure your dogs head as you would slip on the collar. The diameter when open is the size you would need. If you want more instruction, just email me and leave me a number where I can reach you. I will be glad to call so you get the right size.

16" and 18" the double row measures 1/2" wide

20", 22" and 24" measure 3/4" wide