Expert Insights

How to prepare baby formula— The ultimate pediatrician’s guide to make, mix, warm and store a baby bottle


Many parents, whether they are new parents or have a child or two already, have questions about how to prepare baby formula. It can be somewhat confusing since infant formula comes in several different types: powder, concentrate and ready-to-feed. Each of these have different formula preparation instructions. The key is to follow these instructions exactly to avoid putting your baby at risk for the fluid, electrolyte and nutrition imbalances that come with improperly made formula. The good news is that once you do it a few times, it becomes second nature and the anxiety that may have been there will fade away. This is true with so many aspects of parenting! We are here to help you become a great baby bottle maker.

How to choose infant formula:

  1. It is very important to make sure the formula meets the US FDA nutritional standards so you know your baby is getting the correct amount of nutrients to grow and thrive. 
  2. Unless a child has a specific food allergy or intestinal condition, a cow’s milk-based iron-fortified formula is the standard infant formula used. Do not use a low-iron formula. Iron is necessary for proper growth and development.
  3. It is best to use a formula with the added polyunsaturated fatty acids DHA and ARA for brain and eye development. 
  4. Many formulas have probiotics (“friendly” bacteria to help establish a healthy gut microbiome) or prebiotics which feed the “friendly” bacteria.

How to open and store a new container of baby formula:

  1. Check the expiration date on the formula can before opening it.  If expired, or if the can is dented, bulging, or leaking, throw it out.
  2. Before opening a new container, wash the top with soap and water, rinse and dry well.
  3. Once a can of powder is open, it should be used within one month.
  4. Once liquid concentrate formula or ready-to-feed formula has been opened, it can be stored, covered in the refrigerator for 48 hours. 
  5. Store unopened cans in a cool, dry, indoor location but not in the refrigerator or freezer.
  6. Once a can of powder is open, store in a cool, dry place as above with the lid tightly closed. 
  7. Once liquid concentrate formula or ready-to-feed formula are opened, store in the refrigerator and use within 48 hours. 

How to make a baby formula bottle:

Part 1: How to make a bottle with powder infant formula

**Powdered infant formula is not sterile and should not be fed to premature infants or infants with immune problems unless directed and supervised by your doctor.

  1. Sterilize bottles, nipples, and caps before using for the first time. You can boil the bottle and accessories in water for five minutes, use a microwave steam sterilizer bag or use a stand-alone electric steam sterilizer.

After the first use, there’s usually no need to sterilize your bottle and accessories. Wash these items with soap and hot water. Bottle and nipple brushes can help you clean nooks and crannies. You can also use a dishwasher. If your baby is younger than 3 months, was born prematurely or has a compromised immune system, you might consider continuing to sterilize feeding items.

2. Clean and disinfect the surface you’re working on.

3. Wash hands well with soap and water for at least 20 seconds and dry them. 

4. Make sure you read the instructions on the can because some instructions vary from the standard below.

5. If there is any safety concern about your water, boil water for one minute, then let it cool for up to 30 minutes. This water can be filtered tap or bottled water. It must be potable (safe, drinkable water). If you’re not sure, check with your local health department. If tap water is used, it should be cool, not warm or hot, and let it run for 15-20 seconds to flush out potential impurities. Warm tap water may contain impurities from pipes including lead.  Well water should be tested yearly to check for chemicals and bacteria. 

6. Measure the desired amount of cooled water into the bottle. 

7. Add powder to the water. The typical ratio is one level (not packed) scoop of powder for every 2 oz. water. Always use the original scoop that comes with the can and follow the directions. 

8. Put the nipple and cap on the bottle and shake and swirl well until the powder is mixed. 

Part 2: How to make a baby bottle with concentrated infant formula

This type of infant formula comes as a liquid that is concentrated meaning it is typically double the strength of what the infant should ingest so it must be diluted with water. It is basically made by just adding the proper amount of water and shaking. It is a bit easier, neater, and more convenient than powder but is also more expensive as it’s partially ready to serve. 

Follow steps 1-6 from above, ‘Steps to prepare powder formula infant bottle’.

7. Shake the bottle of concentrated formula well. 

8. Pour the proper amount of formula needed into the bottle. Typically, equal parts water and formula are used, but be sure to read the directions. For example, if making a 4 oz bottle, usually you will add 2 oz of the concentrate to 2 oz of water. 

9. Attach the nipple and cap to the bottle and shake well. 

Part 3: How to make a baby bottle with Ready-to-feed infant formula

Ready-to-feed infant formula is the easiest option. There is no mixing and no measuring of components required. This product is sold in various size options from 2-3 oz bottles to 6-8 oz cans and even 32 oz containers. This option is often the most expensive since it’s ready to serve. 

Since there is no mixing required the steps to prepare are fewer:

Follow steps 1-4 from above, ‘Steps to prepare powder formula infant bottle’.

5. Shake the can of formula.

6. Pour the desired amount of the ready-to-feed formula into a bottle.

7. Attach the nipple and cap, shake, and it’s ready to go. 

How to prepare and fill several bottles of infant formula at once:

If you’d like to prepare formula in advance, you can make individual bottles or use a formula pitcher or other type of batch maker. Please follow the below instructions.

  • Label each bottle with the date and time that the formula was prepared.
  • Refrigerate the extra bottles until you need them.

How to warm a baby bottle:

  • Many babies prefer warm formula but some like it on the cooler side. Either temperature for a bottle is OK. Bottles can be warmed by holding it under warm running tap water or by placing it in a bottle warmer or in a container of warm water for 5-10 minutes. Never microwave formula. It can affect the ingredients, and it can cause hot spots in the fluid which may burn the baby’s mouth. 
  • Test the temperature of the formula by placing a few drops on the inside of your wrist. It would feel warm, not hot. 

Serving and discarding baby formula:

  • Use prepared formula within one hour from when feeding begins and within 2 hours of preparation.
  • Discard any prepared powder formula that has been in the refrigerator more than 24 hours. 
  • Once open, concentrate or ready-to-feed formula can be stored in the refrigerator for up to 48 hours.  

Can you use milk in baby formula? No.

Regular cow’s milk is not suitable nutrition for an infant under a year of age which is why cow milk based formula was created with the precise amount of nutrients a baby needs. Adding milk to a bottle instead of water would completely change the composition of the formula and could cause nutrient deficiencies. 

The content on this site is for informational purposes only and not intended to be a substitute for professional medical advice, diagnosis or treatment. Discuss any health or feeding concerns with your infant's pediatrician. Never disregard professional medical advice or delay it based on the content on this page.

The content on this site is for informational purposes only and not intended to be a substitute for professional medical advice, diagnosis or treatment. Discuss any health or feeding concerns with your infant’s pediatrician. Never disregard professional medical advice or delay it based on the content on this page.

Meet the Author

Lauren Crosby

Lauren Crosby, MD, FAAP is a board-certified pediatrician. She went to medical school at UCLA, and did her pediatric training at Cedars-Sinai Medical Center in Los Angeles. Dr. Crosby is an AAP spokesperson and Bobbie Medical Advisor.

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