Calculating How Much Breast Milk to Put in a Bottle

If you breastfeed, you don't know how much breast milk your baby is actually getting each time she nurses. So, if you're not going to put her to the breast for feeding, how do know how much breast milk to put in a bottle? Here's how to figure it out. 

You want to make sure that you're not overfeeding your baby when you give him a bottle, so here's a 3-step breast milk calculation that can help you figure out approximately how much breast milk your baby should take at each feeding.

1. Convert Your Baby's Weight Into Ounces

One pound equals 16 ounces, and don't forget to add in those extra ounces! So for example: If your child weighs 8 pounds 4 ounces, you convert 8 pounds to ounces (8 x 16 = 128) then add the four extra ounces (128 + 4= 132). So, your baby weighs 132 ounces.

If you use kilograms, multiply your baby's weight in kgs by 35.2 to get ounces. So, using the example above, a baby weighing 8 pounds, 4 ounces converts to 3.74 kg: 3.74 kg x 35.2 = 132 ounces.

2. Divide by 6

Take your child's weight in ounces and divide that number by 6 (132 / 6 = 22). This figure represents how many ounces of breast milk that your baby should be getting in one day. Based on the weight above, this child should be taking in about 22 ounces of breast milk in a 24 hour period.

3. Divide by 8

Now you need to take the total number of ounces per day and divide it by how many feedings your baby will get each day. A newborn or young infant should be eating at least every 3 hours which is eight times a day. So, take the number you just calculated and divide it by 8 (22 / 8 = 2.75 ounces).

If you prefer to use milliliters, then one ounce = 30 ml. In this case, the baby should be taking approximately 2.75 ounces (82.5 ml) of breast milk at each feeding. So, you can put 3 ounces or 90 ml of breast milk in the bottle to feed a baby who weighs 8 lbs 4 oz (3.74 kg). 

The first day or two, your baby won't get much breast milk since you're only producing a small amount of colostrum. But, any amount of colostrum that you can pump and give your baby is beneficial. Between the second and sixth day, your milk production will increase and your newborn may take approximately 2 to 3 ounces every 3 hours (14 to 28 ounces per day). Then from 1 month and 6 months, your baby will take an average of 3 to 3 1/2 ounces every three hours (25 oz - 26 oz of breast milk each day). 

Remember, these calculations are just an estimate and a recommendation of the amount of breast milk that your child should be getting at a minimum of every 3 hours. However, some babies may be interested in taking more than the calculated amount. Plus, as your baby grows and gains weight you will need to adjust your calculations.

You will also need to adjust the amount of breast milk that you put in a bottle when you increase the time between feedings. For example, if your child goes from taking a bottle every 3 hours to every 4 hours, you will need to increase the amount of breast milk in each bottle. So, if your baby was taking between 3 and 3 1/2 ounces every 3 hours (8 times a day), you should adjust the amount in the bottle to approximately 4 1/2 ounces every 4 hours (6 times a day). Of course, if you have any questions or concerns about how much breast milk your child needs, you can always talk to your baby's doctor.

If you will be collecting and freezing your breast milk to bottle feed your baby, it's better to store your milk in 2- to 4-ounce portions especially when your baby is younger and not taking large amounts of breast milk. Storing in smaller amounts prevents waste. It's easy to thaw an extra 2 ounces if you need it, but if you thaw and warm a container with 6 ounces of breast milk and your baby takes 4 ounces, then you have to throw away the extra. Once your child gets older and is taking more at each feeding, you can store larger amounts in each container.