Believe it or not, the size of your breasts has nothing to do with your breast milk capacity. You can have small breasts and be able to store a lot of milk, or you could have larger breasts and a low breast capacity.
Breast storage capacity is simply the volume of milk your breasts can hold at one time. The average breast capacity is about 2-4 oz per breast, although this can vary.
Notice that storage capacity is not the same as the ability to produce milk. Milk production is all about supply and demand: Nursing increases a mother’s levels of prolactin.