Aha! One of the things you won't read about Newfs is that most of them possess the power of telepathy and are master con artists when it comes to food. Not all, but the majority. Don't look in those big, liquid, brown eyes when you dish out his food or he will surely take control of your mind. And Newfs will easily get fat if you let them.
Seriously, though, if you feed a high quality adult food, he won't need to eat tons to get good nutrition. But don't cut back too much. Puppies need more than adults and each dog is different. If you can feel his ribs without too much pressure, he's probably at a good weight. A general rule of thumb is 10 lbs of weight times their age in months up until they are around 9 or 10 months old or so. After that, they simply have to mature and fill out. They also tend to go through growth spurts, which slow down as they start to reach adulthood. So the 10 lb rule is not written in stone. It's just an average.
Also, remember that a dog is programmed to reach a certain size or weight normal to him based on his genes, and each dog is different. So don't think about how big he's going to be, just concentrate on health instead.
One final thing. Each of us on this board feeds a different amount per day. It varies according to the type/quality of food (including treats), the amount of exercise, and the individual dog. The only way to tell how much to feed is by monitoring each individual dog's weight regularly. Not by the scale necessarily, but by feeling him. You just have to keep an eye on it.