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Storage capacity, milk supply, and breast size, what do they have in common?

This is a very interesting topic, specially for mothers who fear low milk supply. Read this post if you're wondering if you have a low milk supply, or if you simply love learning about lactation!

Breast storage capacity

Storage capacity has a huge impact on the lactating parent’s production of milk and breastfeeding management. Storage capacity is defined as the amount of milk the breast can hold between feedings at full capacity. As you can imagine each breast varies in size and shape, as well as the breast’s ductal and glandular anatomy. Storage capacity cannot be determined by the size of your breast (Daly, et al.,1993).

Each breast is capable of producing and supplying milk. The larger the breasts storage capacity, the longer the time between feedings becomes. These extended periods between feedings will not affect the infants growth or the mothers breast milk supply.

As you may have already concluded, a mother who has a smaller storage capacity, will likely be spending more time with the infant at the breast. These more frequent feedings will help satisfy the babies needs, in addition to emptying the breasts which will help maintain the supply by demanding more milk production (Clark, 2022; Cregan, & Hartmann, 1999).

To help drive this concept home, no pun intended. You can envision yourself driving a car, you’re on your way out of town when you realized you’re out of gas. You pull in to the gas station to full up and are in back of a transport truck. You think to yourself, “ wow it must be great to be able to fill up such a big tank so rarely, traveling must be so convenient”. Finally its your turn, you fill up your tank, knowing well that you will need to stop again to refill.

Breast are very similar, in the sense that the parent with large or small breast capacity will both be able to feed their infants. The gas as well as the breast milk are both going to be consumed. The only question is how long will it be before the breast empty from milk/or the cars needs more gas. No matter what your scenario you will eventually need to refill.

What does this mean anatomically?

More often than not parents come to their lactation support appointments believing that they have low milk supply, when their concern’s are actually stemming from having a small breast storage capacity instead.

A study by Daly et al., (1993) show some mothers have as few as 3 milk lobules/ducts, while others have as many as 15. As a result, the amount of milk that can fit in a woman’s breasts varies – anywhere from 2oz to 5 oz combined from both breasts is average but some women can store as much as 10 oz in one breast. Parents as well as medical professionals should not be comparing milk supply between patients, because

every breast is unique.

Having a smaller breast storage capacity simply means that you just have less milk in your breasts per feeding because you just have a smaller capacity. Therefore it is of upmost importance for you to feed on demand regardless of your breast storage capacity. You are listening to the babies needs, all you have to do is follow their cues to make sure they are getting what they need.

A parent who has a smaller breast storage capacity will have a smaller output. Don’t be concerned about your supply just remember that your capacity does not limit your ability to produce breast milk. Try not to compare yourself with others, or question your own ability to produce milk. Try to remember your baby will let you know if they are not receiving enough milk (Cassidy, 2021).


Telling moms how often to breastfeed is a case by case judgement. This is because it is greatly effected by the breast capacity of each parent (Clark, K. (2022). In a research review by Mohrbacher (2011), she explained that when a parent reaches their storage capacity their brain sends inhibiting messages to stop the production of milk if the milk is not being removed. While a parent with a larger storage capacity will not reach that inhibiting point as quickly because the ducts can hold more.

The parents who has a larger capacity will therefore be able to have longer stretches between feedings.

This can contribute to longer night sleep stretches for the infant, as well as not seeing a decreases in

the milk supply with less frequent milk removal (Hartmann, et al., 1996).

Scientifically speaking, this is due to a concept in breast development called galactopoiesis which is the final stage the breast go through postpartum. This stage involves the uses the endocrine, and autocrine pathways, as well as metabolic control. When milk is removed by means of breast feeding in the autocrine pathway, the suckling not only stimulates the release of oxytocin and its subsequent milk ejection, but it also stimulates the prolactin’s release which results in the production of milk. When the milk is stagnant the breast sends local inhibitory factors to stop milk production (Hartmann, et al., 1996; Peaker, & Wilde, 1987).

The infant will take what ever is available to them at a feed. Which will allow for the parents body to produce more and replace the milk that is being removed.

Is it necessary to wait for the breasts to refill after breastfeeding or pumping?

In regards to storage capacity, waiting to determine the amount of time you need before your breast are refilled is not necessary. Waiting for significant amount of time will actually have the opposite effect on their feedback loop. This will cause the milk production to cease, if the lactocytes/ducts sense the breast does not need more milk it will not be created. Slight stimulation of the breasts will trigger the body to start producing more milk. The higher the demand for breast milk, the faster the production and refill of the milk to the breasts.

We advise “feeding on cue”, this will activate the milk ducts to produce more milk. This is crucial in the first few weeks of life. If the body isn’t demanding a higher milk production, it will be harder for the breasts to produce its highest capacity of milk later on in the breastfeeding journey.

But why does it really matter?

Understanding milk storage capacity of the breasts will help understand how often a baby needs to be nursed. This will help us know why some babies feed more often than others, why our breasts don't feel as "full" as other mothers' breasts, this will help us understand how every breastfeeding dyad is completely unique and how every breastfeeding journey is different because it is based on the baby's needs and the mother's breast storage capacity, among many other factors. Please remember that this information is provided in a general matter, since feeding frequency can also be affected by other factors such as oral dysfunction, tongue-ties, low milk supply, growth spurts, and so on.

The three hour feeding window is not a one size fits all mantra.

Some infants need to eat more frequently, and some can go longer without being feed as frequently.

If a parent knew that they on average they produced 3 ounces at each feeding, they would be breastfeeding 9-12 feeds through out the day. The higher the storage capacity the less frequent you would need to feed during the day.

How can one determine their storage capacity?

Many parents have a misconception that the milk that they pump is an accurate representation of the milk they stored in their breasts. This is not so, alternatively there are other tool to help parents determine their milk production productivity. Nancy Mohrbacher (2011), has coined a phrase “The Magic Number” as a tool to help parents learn about breast storage capacity. The magic number refers to the breastfeeding or

pumping sessions that are needed to keep the breasts milk production at maximum output.

Think back to a day where you were comfortable breastfeeding, and your baby thriving. Can you remember how many times you were feeding your baby?

Obviously, this number will vary of the breastfeeding journey and due to the needs of your infant.This number will fluctuate, and if your find that you are dropping below your preferred magic number, you will also find that your milk supply will decrease.

Can the breast storage capacity change over time?

In a way yes, and no. During a single breastfeeding journey with ones first child, the breast storage capacity will not change, although with subsequent pregnancies the glandular tissue will continue to grow contributing to a larger milk storage capacity. In addition, those who suffer from insufficient glandular tissue may find that they can produce more milk because of glandular growth with subsequent pregnancies.

At this point of the blog you are probably wondering where you fit in on the scale of things.

Nancy went on to create a graphic of the following information that I will explain for you.

Imagine your infant is between 1-6 months, the average intake per day is around 30 ounces. Decide where you fall in the grand scheme of breast storage capacity.

  • 12 FEEDS

Does your baby take both breasts? but wakes up often during the night to feed. When you pump you generally get less than 4 ounces.

You have a small storage capacity.

  • 8 FEEDS

Does your baby take one or both breasts during a feed? May need to wake up during

the night to feed, when you pump you have the ability to yield 4 ounces in one sitting.

You have a medium storage capacity.

  • 6 FEEDS

Does your baby only take one breast, and becomes satisfied with its supply very quickly? Does your baby often sleep through the night? When you pump are you yielding more than 4 ounces?

You have a large storage capacity.

Later down the line: Infants have the ability to demand more milk production and storage capacity. As a rule of thumb, always remember that a parent’s milk production depends on infant demand and the draining of the breasts.

If you are unsure if your baby is receiving enough milk per feeding, please reach out to

us at Mamas Au Lait for additional assistance with your breastfeeding journey.

Book an appointment here.

By Deena Zacks.

Edited by Paola Vallarino.


  • Cassidy, D. (2021). Is it low milk supply or small storage capacity? Dianne Cassidy Consulting. Retrieved October 26, 2022, from

  • Clark, K. (2022). Breast Milk Storage Capacity 101: A simple guide for breastfeeding moms! The Breastfeeding Mama. Retrieved October 26, 2022, from

  • Cregan, M. D., & Hartmann, P. E. (1999). Computerized breast measurement from conception to weaning: clinical implications. Journal of Human Lactation, 15(2), 89-96.

  • Daly, S. E., Owens, R. A., & Hartmann, P. E. (1993). The short- term synthesis and infant-regulated removal of milk in lactating women. Experimental Physiology, 78(2), 209-220.

  • Hartmann, P. E., Owens, R. A., Cox, D. B., & Kent, J. C. (1996). Breast development and control of milk synthesis. Food and nutrition bulletin, 17(4), 1-12.

  • Kent, J. C., Mitoulas, L., Cox, D. B., Owens, R. A., & Hartmann, P. E. (1999). Breast volume and milk production during extended lactation in women. Experimental physiology, 84(2), 435-447.

  • Mohrbacher, N. (2011). The magic number and long-term milk production. Clinical Lactation, 2(1), 15-18.

  • Peaker, M., & Wilde, C. J. (1987). Milk secretion: Autocrine control. Physiology, 2(4), 124-126.

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