I don't give them any set amount. I just try to feed them when they are hungry and not let them do any "recreational" eating. Some cats will eat just for something to do if they are free fed or fed more than they need to survive. I like to go by how they look too. Cubby is not overweight at all, but he's finicky. I can put meat out after he meows at me, asking for food, and he will walk away from it and Luke will eat it if I leave it there. But when Cubby decides he's ready to eat, he will eat a chunk of meat and ask for more in 10 minutes, and I will often give it to him. I try not to feed them too much too fast or they may vomit it back up.
I often buy almost outdated organic chickens and freeze them. I have a good meat cleaver and cutting board [be careful not to lop off a finger]. I no longer buy organic pork, it's getting to be too expensive. I buy commercial pork instead, which, IMHO, is still way better than canned or dry foods.
If I was going to feed them canned food, I'd find one with no grains.