Well, Kipawa is now 17 weeks old. His neck to tail length is just under 15". So, by the measurements you have given, I would suggest the 12-14" for your pup, which will give you a bit more use out of the sweater. They grow so fast! Also, depending on you getting a male or female pup, one thing I found out when buying Kipawa a raincoat is that a lot of the coats and sweaters out there don't provide enough clearance for a male dog peeing (the pee would wet the coat). We had to try on several to get the correct fit.