There are puppy weight prediction charts on websites you can google. They will also be breed specific sometimes. These are loosely accurate at best. We also can provide you a guesstimate off current weight, parents weight, and weight prediction websites.... but keep in mind there's plenty of factors at play when it comes to predicting an 8 to 12 week old puppy and then the adult weight. It's similar to looking at a human baby and predicting adult weight... you can look at current weight, parent weights, but it may not be wholly accurate due to factors which change with longer periods of time.