It's going to vary from kid to kid depending on how much they weigh. The easiest way is to determine how much to feed is to weigh the baby, convert his/her weight to ounces, multiply by 10-12% and divide by 4. That is how much to feed at each feeding. For example if the kid weighs 8 ounces multiply 8 by 16 = 128 ounces. 128 times 11% = 14.08. 14 divided by 4 =3 1/2 ounces per feeding every 6 hours.
If you don't have a scale to weigh the kid, weigh yourself on the bathroom scale then pick up the kid and weigh both of you. Subtract your weight from the combined weight of the kid and you and you have a pretty good of what the kids weighs.