Calculating How Much Breast Milk to Put in a Bottle

How to calculate the amount of breast milk per bottle

 Verywell / Cindy Chung 

If you breastfeed, you don't know how much breast milk your baby is getting each time they nurse. 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. 

Calculating the Amount of Breast Milk per Bottle

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

Equation

Your baby's weight in ounces / 6 / 8 = Ounces of breast milk per bottle

If you are using milliliters rather than ounces per bottle, multiply the result by 30.

Step 1: Convert Your Baby's Weight to Ounces

One pound equals 16 ounces (don't forget to add those extra ounces). If your baby weighs 8 pounds 4 ounces, convert 8 pounds to ounces (8 x 16 = 128).

Next, add the four extra ounces (128 + 4= 132). Your baby weighs 132 ounces.

If you are using kilograms, multiply your baby's weight in kilograms by 35.2 to get their weight in ounces.

Using the example above, a baby weighing 8 pounds, 4 ounces converts to 3.74 kg. (3.74 kg x 35.2 = 132 ounces).

Step 2: Divide by 6

Take your baby'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 example above, the baby should be taking in about 22 ounces of breast milk in a 24-hour period.

Step 3: Divide by 8

Finally, take the total number of ounces per day and divide it by how many feedings your baby will get in one day. A newborn or young infant should be eating at least every 3 hours (eight times a day).

Take the number you 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 getting approximately 2.75 ounces (82.5 ml) of breast milk at each feeding.

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). 

How Much Breast Milk Does a Baby Need Each Day?

The first day or two after birth, your baby won't get much breast milk since you're only producing a small amount of colostrum. That said, 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. Your newborn will probably take about 2 to 3 ounces every 3 hours (14 to 28 ounces per day).

From 1 month to 6 months of age, your baby will take an average of 3 to 3 1/2 ounces every three hours (25 oz to 26 oz of breast milk each day). 

Adjusting the Amount of Breast Milk per Bottle

These calculations are just an estimate of the amount of breast milk that your baby should be getting at a minimum of every 3 hours. Some babies might be interested in taking more.

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 baby 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.

If your baby was taking between 3 and 3 1/2 ounces every 3 hours (eight times a day), adjust the amount of breast milk in the bottle to approximately 4 1/2 ounces every 4 hours (six times a day).

If you have any questions or concerns about your baby's feeding schedule or nutritional needs, talk to your pediatrician.

Portions for Storing Breast Milk

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. This is especially true when your baby is younger and not taking large amounts at each feeding.

Storing breast milk 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 only takes 4 ounces, you'll have to throw the extra away.

Once your baby gets older and is taking more at each feeding, you can store larger amounts in each container.

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Article Sources
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  1. U.S. Department of Health & Human Services. Your Guide to Breastfeeding. Updated October 08, 2018.

Additional Reading
  • Lawrence RA, Lawrence RM. Breastfeeding A Guide For The Medical Profession Eighth Edition. Elsevier Health Sciences. 2015.
  • Riordan, J., and Wambach, K. Breastfeeding and Human Lactation Fourth Edition. Jones and Bartlett Learning. 2014.