In general, the dogs are between 19 - 22inches and 14 - 20 kgs, and bitches are 18 -21 inches and 12 - 19kgs
As ever, being under or over these numbers makes no difference unless you intend to Show your dog. At 4 months, your dog has a lot more growing to do. I would say your dog is likely to be at the larger end of the numbers. You can see the growth pattern by looking at my eldest bitch - Milly- here from puppy to adult -
http://www.cbhughes.com/6.html -
Click on Tosca and Storm for the same growth photo show
I have 3 bitches - 2 are 18 inches and 15kg, and the other is 19 inches and 19.5kg. Most people who see them who don't know BC's remark they seem small - not realizing that they are within the normal range rolleyes*