Auburn Leather Crafters Sizing Guide (Standard Buckle and Martingale)
 
Measuring an old Buckle collar: If you are satisfied with the fit of your dog's current collar, measure that collar from the center bar of the buckle to the farthest hole. Our collars are sized according to this measurement, not to the over-all length of the collar, which varies by manufacturer and by whether it is a buckle-end or a dee-end style collar. (see diagram below):
Auburn Collar Size
 
 
 
Measuring you dog's neck: For a standard buckle collar, the collar size is approximately the distance from the center of the buckle to the last hole. To calculate the correct collar size, take the exact (comfortable) measurement around your dog's neck and add 2". This is the collar size you need.
 
For a Martingale collar, the collar size is approximately the distance around the collar at its center opening. To calculate the correct collar size, take the exact (comfortable) measurement around your dog's neck. Then round up to the collar size that is above the measurement that you took on the dog's neck. This is the collar size you will need. Do not measure the old collar.  
Martingale Note: Make sure the widest opening will fit around the dog's head when attaching the collar.
 
Examples:
  1. If your dog's exact (comfortable) neck measurement was 12", you would round up to the collar size 14". This would be the size 14 collar.
  2. If your dog's exact (comfortable) neck measurement was 15.5", you would round up and pick the collar size18".
  3. If your dog's exact (comfortable) neck measurement is exactly in between two sizes, then pick the smaller size. The collar will stretch slightly with wear.