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How To Use Breast Milk Bags & How Many Do You Need

How To Use Breast Milk Bags & How Many Do You Need
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Here is an easy guide on how to use breast milk bags. I’ve also included all the best tips so you don’t waste any bags, and how to calculate how many breast milk bags you will need.

A few different ways you can use breast milk bags are:

  • Pumping directly into the bags
  • Using milk bags for short term storage in a refrigerator or cooler bag
  • Using milk bags for long term storage in a freezer

The Most Common Reason To Use Breast Milk Bags

The most common reason you may use milk bags is to create a freezer stash. If milk bags are frozen flat, then they can be packed neatly together so they take up less space in your freezer.

Another benefit of using breast milk bags in the freezer is that they can be frozen in small increments. After thawing the milk, you have to use it within 24 hours. 

This means it is beneficial to freeze in 4 to 5-ounce increments so you can thaw the exact amount your baby will eat at each feeding.

My favorite brand of milk storage bags was easy to use because I could pump directly into them. They were thick and durable.

Most importantly, they didn’t leak when I defrosted them. There is nothing worse than losing the liquid gold that you worked so hard to pump.

Here is a link to check out my favorite brand of milk storage bags (on Amazon). If you see them on sale, I’d definitely stock up.

More Reasons To Use Breast Milk Bags

Here are a few more reasons you may need to use breast milk bags. 

  • As a backup in case you pump extra milk or your bottles are dirty
  • When traveling to save space in the cooler
  • To save time cleaning bottles
  • To bring milk to the hospital (if you have a preemie in the NICU)

Reason #1: As A Backup

I kept a few extra unused breast milk bags at work, in my pump bag, and at my pumping station at home.

These were my backup in case I ever forgot bottles or if I pumped extra milk that wouldn’t fit in the bottles I brought with me. 

The extra milk bags were also useful if something happened to my bottles. I didn’t want to accidentally drop a bottle on the floor and then be stuck without a clean place to store milk. 

You may use breast milk bags if you do not have enough bottles, or if you do not have any clean bottles available. It might be the middle of the night and storing milk in a bag is easier than using bottles.

Reason #2: When Traveling

Another one of my favorite reasons to use breast milk bags was when I was traveling. I took milk with me on an airplane and it was a lot easier to bring milk bags.

This is because space in my cooler was tight, and I could fit more milk in my cooler if they were in bags instead of bottles.

It also was easier to cool down the milk to the correct temperature than if the milk was in a bottle in the cooler.

Reason #3: Pump & Feed From The Same Bag

You can also pump directly into breast milk bags, and feed directly from those bags.

This was one of my favorite time-saving hacks when I was exclusively pumping. It reduced the mountain of dirty bottles to clean at the end of the day.

I used the Kiinde system to pump into and then feed out of the same bags. 

If you want to check it out, you can try the starter pack for free (just pay $6 shipping). This offer isn’t publicly available on their site, but you can get it by clicking this link. You also get a couple of awesome coupons when you order the free starter pack.

Reason #4: If You Have a Preemie

The last reason you may want to use breast milk bags is if you have a preemie. When my daughter was in the NICU, I used breast milk bags to bring her milk to the hospital.

I pumped and brought milk in bags with fresh (never frozen) milk. This won’t apply to most moms unless you have a preemie.

How To Use Breast Milk Bags (Step-By-Step) 

Here are the eight easy steps to follow when you are using breast milk bags.

1. Start by pumping or collecting milk

You can either pump directly into bags, or pump into bottles and then transfer the milk from bottles into bags.

For more details on pumping directly into bags, check out this article.

If you are collecting milk with a Haakaa, that works as well

2. Carefully transfer milk from bottles into the milk storage bags

I like using a funnel that is food grade and BPA free to transfer milk. 

If you don’t have a funnel, you can use a Medela breast shield as a funnel (like this one from Target).

You can skip this step if you pumped directly into the storage bags. 

3. Label your milk storage bag with the date and number of ounces 

Labeling your milk with the date will help you to know when the milk expires.

Pro Tip: I used a food scale to weigh the number of ounces in each breast milk bag. I found this was more accurate than the markings on the milk bags.

4. Put the bag of breast milk in the freezer

If your milk storage bag is full (around 4 to 5 ounces), then it is ready to go into the freezer.

If the milk bag isn’t full, then zip or twist it shut and put it in the refrigerator until you have more milk from your next pumping session to fill up the bag.

5. Use a dedicated flat surface to freeze your milk bag

You can use a meatloaf pan like this one (it is the perfect size for one bag). 

Or, if you really want to maximize your freezer space, you can use a tool like this to get your bag as flat as possible.

6. Review the CDC’s guidelines for breast milk storage

Milk that has been in the freezer is good for 6-12 months.

7. Thaw the breast milk bags when you are ready to feed

When thawing breast milk bags, you can thaw it in the refrigerator or in lukewarm water.

After it has thawed, then the milk needs to be consumed within 24 hours or thrown out.

8. Transfer the milk from your storage bags into bottles

Check out this article for detailed instructions on transferring breast milk from bags to bottles so you don’t spill a drop of your liquid gold.

Now that you know how to use breast milk bags, it is time to calculate the number of milk bags you will need during your breastfeeding journey.

How Many Breast Milk Bags Do I Need?

You may need anywhere from 50 breast milk bags up to 600 (or more) bags. Follow these three steps to determine how many breast milk bags you will need.

Step 1: “In Case of an Emergency” Milk Bags

The first part of the equation are the bags you will need “in case of an emergency”.

I liked to keep 5-10 breast milk bags in each of these places:

  • At work
  • In my pumping bag
  • In my car, and 
  • At my pumping station at home

Those breast milk bags were my stash that I kept on hand at all times. I wanted them close by so I always had a clean bag to store my milk.

Trust me, you do not want to be stuck at work and realize you forgot your bottles.

Or, you might be pumping in the car and pump an extra 5 ounces more than what your bottles will hold. You’ll definitely want to have a few milk bags on hand for when something like this happens to you.

I usually kept around 50 breast milk bags on hand for this purpose.

Step 2: Calculate the Number of Breast Milk Bags While Traveling (And Away From Baby)

The next part of the equation is the number of bags you will need if you have an upcoming trip.

If your baby will not be traveling with you, then you will need to bring enough breast milk bags to store the milk you pump during your trip.

First, calculate the number of ounces you pump per day.

For an average milk supply, you’d pump around 30 ounces per day. This means you’d need at least 6 bags per day, plus a few extras in case one gets dirty or leaks. 

I liked to bring at least 10 bags per day of a trip so I didn’t have to worry about running out and finding breast milk bags at a store while I was traveling.

As an example, say that you plan to breastfeed or exclusively pump for a year. During that time frame, you go on two trips that are 3 days each.

To store your milk while you are traveling on these two trips, you’ll need bags for 6 days or 180 ounces of milk. If each bag holds 5 ounces, you’ll need 36 bags. Then, add on a few extras to have on hand.

This equates to about 40 to 60 breast milk bags.

Step 3: Calculate the Number of Breast Milk Bags For Freezer Storage

The next part of the equation is to figure out how many you will need for long term storage. This will depend on your milk supply and your freezer space. 

For example, you may have a slight over-supply of breast milk and pump an extra 5 ounces per day above what your baby eats. In this case, you’ll need 1 extra bag per day (or 30 per month). Over the course of 9 months, you will need about 270 bags.

Here is a second example. You might have a large oversupply. You are freezing milk that will feed your baby for 3 full months. 

In this case, you need enough bags to store 3,000 ounces. This means you will need about 600 bags if you freeze in 5-ounce increments.

Now you can see where you may need as low as 50 breast milk bags to have on hand in case of an emergency. Or, you may need 600 or more milk bags if you have a large supply and store tons of milk in the freezer.

More Pumping Tips

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NEXT, check out these articles for more tips

  1. How To Use A Spectra S1 and S2 Pump (with Bonus tips!)
  2. The Crazy Number of Calories Pumping Burns
  3. How Often Should You Replace Pump Parts?


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