How much milk does my baby need?

In exclusively breastfed babies, milk intake increases quickly during the first few weeks of life, then stays about the same between one and six months (though it likely increases short term during growth spurts). Some breastfeeding research does not indicate that breastmilk intake changes with baby's age or weight between one and six months. Breastmilk intake will continue at this same level until -- sometime after six months, depending in baby's intake from other foods -- baby's milk intake begins to decrease gradually.

Studies found that average breastmilk intake to be:
750 ml per day between the ages of 1 month and 6 months. Different babies take in different amounts of milk in typical range of 570-900 ml per day.
875 ml per day at 7 months
550 ml per day at 11-16 months.
400-550 ml per day between 12 and 24 months
300-360 ml per day between 24 and 36 months

There is also a formula for estimating the amount of milk to offer a breastfed baby at a feed. Take your baby's weight (in pounds) and multiply by 2.5 (oz). Or take your baby's weight (in kg) and multiply by 156 ml. Divide by the average number of feedings in a 24-hour period. This will equal the amount of mother's milk per feeding. Remember that this is theoretical -- all babies are unique and have different needs.

Formula:
1 pound of weight needs 2.5 oz
1 kg of weight needs 156 ml

Sources:
http://www.kellymom.com/bf/pumping/milkcalc.html#solids
http://www.onlineconversion.com/weight.htm