It depends on your fish. No-one should be able to tell you that this magic number is the right thing for your individual animal. Though that would be nice, I totally agree! :)
I feed my guys NLS, which are very tiny, and my bettas are quite large and most do quite a lot of swimming, so I feed a fair amount of pellets. I actually don't keep count, just a few at a time twice daily.
I feed them until they look round, like they're full. Then I make sure that they are back to being sleek again before I feed them the next time. If they're still overly around, I fast them a day, and cut down their food on subsequent feedings.
How much you feed is going to change over time. It's going to depend on your fish, the size of their tank, their metabolism, their age, how active they are, so on and so forth. Because of this, feeding should be less about a certain number, and more about watching your animal and making sure that they are healthy. You are not going to give your betta SBD or Bloat by overfeeding a couple of times, and it is fairly obvious that they're getting too round if you watch them carefully. They are going to be rounder following a feeding, but should have returned to sleekness by the next one if you have found the right number. :)
If your guy looks too round right now, fast him a day or two, and then play with his food, going back and forth between amounts and how often you feed him. At some point you'll find the right balance and he'll be good for awhile. :)
I hope that helps!!