The amount of breast milk or formula your baby eats in a single feed will increase as they grow and develop. For instance, while a newborn can only stomach a teaspoon or so of milk during their first feeding, this will increase to 2 whole ounces by the time they're 2 weeks old!
Broadly speaking, your baby will be able to eat 4 ounces per feeding by the time they're 3 or 4 months old, but don't take this number too seriously.
All babies are unique, and while one parent might find that their 5-month-old can just about manage 4 ounces, another might discover that their baby wants more than this at 3 months!