Small/Medium Collars are 3/4" wide and adjust from 11" - 15"
Medium/Large Collars are 3/4" wide and adjust from 15" - 20"
How to measure your dog's collar size
Use a soft measuring tape and measure the widest part of your pup's neck. Place two fingers between your dogs neck and the measuring tape to ensure a comfortable fit.
For growing dogs or dogs with an extra thick coat, you may consider using three fingers instead.
If you don't have a soft measuring tape you can use a piece of string instead and then measure that against a ruler or hard measuring tape.