Corso Size?

I see so many different sizes out there and just like people breeds can greatly range in size. Last week at 21 weeks old Bruce Wayne was 76.2 lbs. Is there a ACCURATE growth chart out there? Or anyone with a similar aged pup to compare. He has gained roughly 5lbs a week since we got him. He is about to outgrow the feeding chart on the puppy food. What do I do when he does? Just slowly add a 1/4 cup as he grows? Eyeball him to make sure he is staying lean?