So at nine months, he's going to be pretty well full grown.....so presuming he has a coat and you can't see his ribs, can you feel them? can you feel his spine? Is he lively and active? Coat shiny and healthy looking? It genuinely hard to say a dog should have "this much" food. I have got two dogs who are litter brothers. One needs to be given around a third more food than the other to keep condition on him. He is an idle devil whose favourite thing is to kip. His bro, who is more squarely built (takes after Mum not Dad) is constantly on the go and would spend the whole night out in the garden hunting if I let him, can get chubby quite quickly if I am not careful. Both weigh a lot more than the vet's chart says they should yet I can see the ribs and the spine on idle boy and his bro is solid muscle. Seriously the only way to tell how much food to give is to know your dog and how they should look/feel. If he looks and feels fine, enjoys his food, runs and plays without wheezing or limping and doesn't make masses of poo then you are golden.