He eats between 3-4oz every 2-3 hours. Every day is different. Sometimes he's 2 hours on the spot, sometimes he lollygags and it'll be 3.5 hours. Sometimes, he'll eat 4oz and still be hungry, sometimes he's alright with 4oz.
I wouldn't be worried if I was you. He'll eat when he's hungry. Follow his cues, feed him when he's hungry, and stop feeding him when he shows you that he's done eating. PP is right, he won't starve himself. As long as he is having wet diapers, he'll be alright. Ease up and just let him do his thing, you'll probably have a much happier baby...and he might STTN then! :)