It's hard to gauge by size. I am friends with one of the families who adopted Jersey's sister. Jersey is about 16-17 inches tall and weighs about 40 lbs. She's a big Beagle girl. Gidget, her sister, is about 3-4 inches shorter than Jersey and only weighs about 30 lbs.
If your vet says the same thing the breeder told you, then it's most likely correct. You could always try a different vet to see what they say, but why waste the money? I''ll see if I can find the paperwork from when Jersey was a puppy to see what her weight was (I save all that stuff...I still have Amber's stuff and she passed to the Bridge almost 4 years ago).