The general formula for predicting adult size is to multiply their height at 8 to 10 weeks by 1.5 give or take 1 inch. It's difficult to give you a size that they should be at 4 months because they are still maturing, and puppies will mature at different rates. Predictions on adult size and proportions can be best made at 8 weeks, as the puppy is as close to its adult proportions at 8 weeks as it will ever be until it is an adult. You should contact your breeder, as they would be able to give you the best prediction based on the size of the parents and the size of puppies from previous litters.
Answered by jgilje - 8/3/2011 4:34:13 PM