Everything you need to know about how to prep formula

Janel F., MS, RD, LDN

When you think about bottle feeding, you might imagine confident parents mixing formula with one hand while cuddling their baby with the other. But what we are actually confronted with is an onslaught of contradictory information on how to prepare formula. To boil or not to boil? What type of water should I use? What formula do I use? Do I swirl or shake? A lot of it depends on your baby, your family’s preferences, and even the area you live in. Read on to get all of your questions answered!

What water should I use in the formula?

The type of water you use can depend on a number of factors.

If you live in an area with good water quality (you can often easily find your city, town, or county’s water report online), you’re typically fine to use your own tap water. You can use filtered water, but if you live in an older house with lead pipes, ask your baby’s doctor what the best course of action is.
Some cities and towns add fluoride into their water, which can be great for baby’s growing teeth. However, formulas also contain fluoride, and this may lead to a slightly increased risk for milk fluorosis, or white markings on their teeth. More information can be found here: https://www.cdc.gov/fluoridation/faqs/infant-formula.html
If your household uses well water, you may be better off using bottled or nursery water.

Do I need to boil the water for formula?

The recommendation to boil water stems from the small chance that non-sterile powdered formula may contain a bacteria called cronobacter. Many organizations, including the CDC, WHO, and WIC, recommend that babies who were born prematurely, babies less than 3 months old, and babies who have weakened immune systems use either liquid formula (concentrate or ready-to-feed) or boil water prior to mixing it with powdered formula. Once boiled, let it cool to “no less than 158°F/70°C before pouring it into a clean and sterilized feeding cup with a lid, or bottle. Water should cool to this temperature within 30 minutes after boiling” (source: CDC). At this temperature, mix the formula as you usually do, allowing it to cool to body temperature before feeding to baby. Always test the temperature by placing a few drops on your wrist.

Babies who are full-term, over 3 months old, and do NOT have weakened immune systems can use powdered formula without following the above directions.

How do I prep formula?

While parents often use powdered formula, many brands also offer it in concentrate and ready-to-feed versions, which do not require the same preparation. Ready-to-feed containers are convenient but more expensive.

Remember to always use clean and sterile containers, and to wash your hands well before handling or preparing formula.

Concentrate formula

Concentrate formula is often prepared using a one-to-one ratio. You can batch prepare concentrate formula ahead of time, which you can then store in the refrigerator for up to 24 hours. Simply pour the concentrated formula into a clean and sterile storage container or pitcher, and then pour an equal amount of water in. Make sure to read the directions on the side of the container of concentrate formula you are using to double-check preparation instructions.

Powdered formula

Powdered formula is most often prepared* by using 2 ounces of water for every scoop of formula. Here are specific instructions:

After washing your hands and prepping the water if necessary, pour into the bottle the amount of water you wish to use. The amount of water should be however many ounces you wish to prepare. **Note that it is recommended you prepare formula in even-numbered ounces only (for example, 2 ounces, 4 ounces, 6 ounces, etc., and NOT 1 ounce, 3 ounces, and so on). This is because you cannot get an exact half-scoop measurement, and you may wind up over- or under- concentrating the formula.
After you pour the water into the bottle, use the scoop only from the container of formula you are currently using and scoop the formula. Tap it lightly on the side of the canister to even it out. You don’t want to pack it down, but you also don’t want it overflowing. The following chart will be helpful in determining how many scoops you need:

If you want:	Use this many ounces of water:	Use this many scoops of formula:
2 oz of prepared formula	2 ounces	1 scoop
4 oz of prepared formula	4 ounces	2 scoops
6 oz of prepared formula	6 ounces	3 scoops

After capping the bottle, gently shake the formula until well-mixed. Some formulas may be more sudsy or foamy than others, but this is normal.

** If your baby has special medical needs or is premature, your doctor or dietitian may recommend a different recipe for formula prep. If you are mixing formula with breast milk, most of the time you prepare the formula first, then mix with the breast milk. Do NOT make formula using breast milk as the liquid, unless directed otherwise.

It is VERY important that you don’t water down formula or add more powder than necessary. This can be VERY dangerous for your baby. If you need help with buying formula, contact your local WIC office, or call 211 (in most states).

Here are some other resources to check out:

How to choose a formula?

It’s important to remember that all formulas sold in the United States are made under strict standards and regulations. Which you choose comes down to personal preference, or if you are on WIC, what formula your WIC agency offers.

You may see different formulas touting different benefits, but in reality, whatever formula you choose, if it’s sold in the US, you can be assured it is the right nutrition to help your baby grow.

Unless otherwise directed, it is normal to start out with a standard cow’s milk-based formula. Remember that gas is normal in newborns, and constipation is normal in babies fed formula for the first time. In fact, formula-related constipation can last up to a month or so, but even though it can be normal, its still best to inform your pediatrician. It’s also best not to keep switching formulas unless directed by baby’s doctor.

Do I need a bottle warmer?

Bottle warmers aren’t always necessary, especially if you are boiling the water first. Some babies do take a warmed bottle easier, though keep in mind if that baby gets used to warm bottles it may become difficult to feed on the go!

NEVER heat the bottle in the microwave. This can create dangerous hot spots in the milk that could scald your baby’s tongue.

You can always make your own bottle warmer by placing the prepared bottle in a bowl of warm water.

Formula storage quick tips

Prepared or open ready-to-feed formula must not be kept out of the fridge for longer than 2 hours.
Prepared formula can be kept in the fridge for 24 hours.
If baby has already taken milk from the bottle, any leftover milk in the bottle must be discarded after 1 hour.

How much formula does baby need?

Newborns have tiny bellies, so they may need small amounts more often. It’s best to listen to baby’s signals, feeding when they show hunger and stopping when they indicate fullness. Preparing formula in smaller amounts may help if bottles are not being finished – you can always prep more if needed!

Feeding baby upright instead of the classic laying down position can help baby regulate their intake better. Additionally, letting baby take some breaks during the feed will allow them to stop when full. Keeping the bottle horizontal also helps slow down the pace of the feeding and lets baby be more in control.

Most newborns start out at 2 ounces or so per feed and will gradually increase. Per the American Academy of Pediatrics, your baby should be taking in around 2 ½ ounces of formula per day for every pound of weight. So for a 9 pound baby, this would be around 22-24 ounces of formula per day.

Formula does take longer to digest, so you may see your baby goes longer between feeds than their breastfeeding counterparts. Just listen to baby’s cues! Learn more at Baby Hunger & Feeding Cues.