What how much formula should my 9 month old drink?

24-32oz. On top of that he may be ready to eat table food not just baby food.
It varies. If you let your baby drink formula each feeding until he/she doesn't want any more, then offer a balanced diet of baby food after each bottle, your baby will take the right amount of each. Most 9 month olds will take 30-35 ounces of formula daily, with enough solids to fill them up the rest of the way.