Marityne Dog Sizing Guide:

 
The adjustable length shown is the distance around the collar from the minimum to maximum adjustment.
 
Size Adjustable Length Comfortable Neck Measurment
Toy-XS 7" to 9" 7" to 9"
Toy-S 9" to 11" 9" to 11"
XS 8" to 11" 7" to 9"
S 10" to 14" 9" to 12"
M 12" to 18" 11" to 16"
L 15" to 23" 14" to 21"
 
Measure the exact (comfortable) size of the dog's neck and add 2" then chose a collar that reflects THAT measurement.
 
For example:
  1. If your dog's exact (comfortable) neck measurement was 12", you would pick a collar adjustable length closest to 14". This would be the S or M collar. For a growing dog the M would give you room to grow, for an adult dog the S collar or the M collar would work.
  2. If your dog's exact (comfortable) neck measurement was 15.5", you would pick the collar adjustable length closest to 17.5". This would be the L collar.

If you are not sure, please call us at 877-800-8181 to speak to a customer service representative.