Rough estimate. Babies consume roughly 1/2 their pound weight as ounces at a feeding after it is well established. For a 8 lb kid that equates to ~ 4 ounces. For breast fed kids I find it better to count diapers than ounces. Too many moms get stuck on quantity & express & bottle feed to watch volume. If baby is wetting a diaper every 4-6 hours and filling out, it is doing fine.
1-2oz. A week old child will probably eat 1-2oz every 1-3 hours. Breast fed babies tend to want to eat more often, usually every 1-2 hours and should eat for about 20 minutes from each breast. A week old child should not go longer than 3 hours between feedings.
No need to know. There is no need to know how many ounces your one week old baby is getting at every feeding. If your baby is nursing well every 2-3 hours and having between 6-10 runny and mustard color stools and equal number of urine, then he must be getting enough breastmilk. I discourage moms who want to pump and place the breastmilk in a bottle so they know how much milk the baby is getting.