Expert Insights

How to Prepare Baby Formula— The Ultimate Pediatrician’s Guide to Make, Mix, Warm and Store a Baby Bottle


Whether you’re a new parent or already have one or two little ones running at your feet, you could have questions about how to prepare baby formula

It may sound straightforward, but it easily becomes confusing since infant formula comes in several different types: powder, concentrate, and ready-to-feed. Each of these has its own unique preparation methods.  

For each type of formula, it’s important to follow the instructions exactly to prevent fluid, electrolyte, and nutritional imbalances that happen with improperly made formula

The good news is that once you do it a few times, knowing how to make a formula bottle becomes second nature, and any anxiety there may have been 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:

There are so many factors that go into choosing the right formula for your baby. Before anything else, you want to ensure your formula is regulated by the United States Food and Drug Administration (FDA) and meets its nutritional standards. This will give you peace of mind that your baby is getting the correct amount of nutrients to grow and thrive. 

Unless your child has a specific food allergy or intestinal condition, a cow’s milk-based iron-fortified formula is the standard infant formula used. It’s best to avoid low-iron formulas as iron is necessary for proper growth and development.

Many formulas also have added polyunsaturated fatty acids– DHA and ARA– for brain and eye development. Some also 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:

Safety starts with the formula container itself. Follow these easy directions to make sure your formula is opened and stored so that it stays fresh and safe for your baby. 

  • Check the expiration date on the formula can before opening it.  If it’s expired, or if the can is dented, bulging, or leaking, throw it out.
  • Before opening a new container, wash the top with soap and water, rinse, and dry well.
  • Powder formula: Once opened, store it in a cool, dry place and use it within one month.
  • Liquid concentrate formula or ready-to-feed formula:  Once opened, it can be stored and covered in the refrigerator for up to 48 hours. 
  • Store unopened cans in a cool, dry, indoor location but not in the refrigerator or freezer.

How to make a baby formula bottle:

Depending on the formula you use, the methods for making your baby a bottle can be quite different. Here are the basic instructions for making a bottle with powdered, liquid concentrate, and ready-to-feed formulas. 

For all types, follow these instructions for preparing your bottle for the formula. 

  • Sterilize bottles, nipples, and caps before using for the first time. There are many ways to sterilize baby bottles— from boiling water to electric bottle sterilizers. Find the method that works best for you.
  • You’ll want to sterilize your bottles if your baby is younger than 3 months, was born prematurely, or has a compromised immune system. Once their immune system is more developed, washing with hot soapy water and air drying is a good way to keep bottles clean. 
  • Clean and disinfect the surface you’re working on and wash your hands well with soap and water for at least 20 seconds. 
  • Make sure you read the instructions on the can because some instructions vary.
  • For powdered formula and liquid concentrate: If there is any safety concern about your water, boil water for one minute, then let it cool for 5  to 30 minutes. 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.

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.

  • Measure the desired amount of cooled water into the bottle and add powder to the water. Always add the water first to ensure the correct amount is used. The typical ratio is one level (not packed) scoop of powder for every 2 oz. water. Use the original scoop that comes with the can and follow the directions. 
  • Put the nipple and cap on the bottle, then shake and swirl well until the powder is mixed. 

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

This infant formula comes as a concentrated liquid, meaning it’s typically double the strength of what your baby should drink. You must dilute this formula with water.

Since all you have to do is pour the formula and water into a bottle, it’s a bit easier, neater, and more convenient than powder.  But, it’s also more expensive as it’s partially ready to serve. 

  • Shake the bottle of concentrated formula well. 
  • 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. 
  • 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 as there’s no mixing and no measuring of parts needed. This product is available in various sizes, from 2-3 oz bottles to 6-8 oz cans and even 32 oz containers. The ready-to-feed formula is often the most expensive since it’s ready to serve. 

Since there is no mixing required, the steps to prepare it are simple:

  • Shake the can of formula.
  • Pour the desired amount of the ready-to-feed formula into a bottle.
  • Attach the nipple and cap, shake, and it’s ready to go. 

Water for baby’s bottle: Boiled, bottled, tap, and temperature

Powdered and liquid concentrate formulas must be mixed with water–but what kind of water is best? 

You can use bottled or tap water, as long as you’ve confirmed that the water source is safe through your local health department or state government agency. If your water source has fluoride added, occasionally mix in low-fluoride bottled water to avoid dental fluorosis– a condition where lacy white markings cover tooth enamel.1

If your baby is under 3 months old, has a weakened immune system, or was born prematurely, you’ll want to boil water from any source before mixing it with formula to kill any germs that could make your baby sick.Boil the water, let it cool for 5 to 30 minutes, then mix the cooled boiled water with the formula. 

Once your baby is older than 3 months and is not at high risk for infection, you can skip boiling the water. Some babies prefer warmed bottles to cold, so if your baby fusses with a cold or cool bottle, just warm it slightly by running hot water out of the tap over the bottle.

Always be sure to shake a bottle and test it on the inside of your wrist if using warmed water to protect your baby’s mouth from burns. 

How to prepare formula in batches in advance 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 up to 24 hours after mixing the formula.

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. You can warm your baby’s bottle by holding it under hot running tap water or 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 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 should 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 if it’s been kept at room temperature. 
  • 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 cow’s milk in baby formula? No.

No. Regular cow’s milk is not suitable nutrition for a baby under a year of age.  Cow milk based formula has the exact amount of nutrients a baby needs. Adding milk to a bottle instead of water would change the composition of the formula and could lead to nutrient deficiencies. 

Can you use breast milk in baby formula?

Yes, you can mix breastmilk and formula together in the same bottle. Some reasons you may be interested in doing this is if you’re transitioning your baby from stored breast milk to formula feeding or have a low milk supply and need to supplement with formula (but don’t want to waste two bottles!). 

If you mix breast milk and baby formula in the same bottle, you must first make the formula with the correct water to formula ratio before adding breast milk. Otherwise, your baby won’t receive the proper mix of water, electrolytes, protein, vitamins, and minerals.  You can mix ready-to-feed formula directly with breast milk. 

Can you add extra water to increase formula quantity?

You may be tempted to stretch your baby’s formula by adding extra water, but doing this could be dangerous for your baby. Adding any additional amount of water to formula can slow your baby’s growth and development and disrupt their electrolyte balance, leading to seizures, according to the American Academy of Pediatrics.2 

Closing thoughts on making a baby bottle

Powdered formula, liquid concentrate, and ready-to-feed formula all provide essential nutrition for your little one, and each one has its own set of rules when it comes to safety. 

From washing the bottle to boiling (or not boiling) the water, getting the temperature right, and mixing the formula– there’s a lot to making a bottle safe for your little one. Thankfully, along with everything else in motherhood, once you do it a few times you’ll be a pro at keeping your baby nourished and healthy. 

Not sure which type of formula is best for your baby? Learn more about how to choose between powdered, liquid concentrate, and ready-to-feed formulas

Verified by: Kelsey Lorencz, RDN


  1. Infant Formula | Centers for Disease Control
  2. How to Safely Prepare Baby Formula With Water | The American Academy of  Pediatrics
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.

This post may contain affiliate links, and we may receive commissions for purchases made from this post.

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.