We do our collar sizing a bit different here.
Size is customized to each and every dog.
Instead of having a collar that adjusts from A to B where your dog could be between sizes, here you provide the neck size and whether or not it is for a puppy or an adult dog.
Measure your dog's neck with a soft measuring tape or piece of string to get the most accurate measurement.
By proving each dog's rough neck measurement, it provides a great fit and also helps to ensure proper embroidery placement.
Measure where and how you like collars to sit on the dog's neck. Some people like them looser some like them tighter.
Measure for the fit you want.
Puppy Collar vs Adult Collar
What qualifies as a puppy collar? What's the difference in the construction?
Any width of collar can be made into a 'puppy collar', it doesn't have to just be the 1" option.
Collars prompt you asking if the dog is "under a year old" or not. Under a year old the dog would obviously require more adjustability than a dog say at 3 years old.
Puppy collars come with the provided neck size as the smallest size available. This allows for plenty of room to grow.
Adult collars can still be adjusted both larger and smaller but growth isn't a huge concern for these collars as they are done growing for the most part. Dogs are mostly just filling out and maturing at this stage and don't require inches and inches of adjustability.
You have two dogs that measure at 14".
Dog A is 5 months old so his collar could adjust from 14-21".
Dog B is 1.5 years old so his collar could adjust from 11-18".
Also, the width of the collar would affect the max adjustability.
Using the same 14" neck for a puppy collar:
1" collar would adjust approximately 14-21"
1.5" collar would adjust approximately 14-20"
2" collar would adjust approximately 14-19"