I know every boxer is different in size but lil Tyson is growing out of collars soooo quick!!! I know the collar I want to get him when he is full size but don't want to spend the money on one he is just going to outgrow so we have been buying cheaper ones until then. He is about to outgrow his 3rd collar now and his neck is around 13 1/2" Here are the collar sizes for the one I want: Medium 14-20"/ Large 18-28" He could fit the medium now but i'm not sure if his neck will get bigger than 20" so I would like to know the size of your full grown, or pretty much full grown boxer neck. Tyson is going to be on the larger size I have a feeling. He is 4 months old and 32lbs so far and his dad was around 90lbs.