Before-and-after weight calculations

How do I use before-feed and after-feed weights to calculate how much milk my baby takes from the breast?

If mothers want to use before-feed and after-feed weights to see how much milk their baby is taking in from the breast, the baby should be weighed before and after every breastfeed for at least one 24-hour period. Total daily intake of breast milk and supplement is measured by calculating the difference between the weights of the baby before and after breastfeeding and adding the amount of supplement taken in. Intake varies from one feed to the next and from day to day. That’s why we recommend doing this over two 24-hour periods. The typical amount of milk and milk supplement that babies need to grow well depends on the baby’s age and size and varies between babies of the same age.

A) How much milk does a baby need?

Please consider working with your health-care providers or a breastfeeding specialist for help with before-feed and after-feed weights (before-and-after weights).

Here is a summary of the typical amounts of milk a term baby needs each day.

This is only a very rough guide as some babies take in significantly less and some take in much more. For example, the reported range of the amount of milk a baby between one and six months takes in is 523 to 1356 millilitres (18-46 U.S. fluid ounces). It is more important that a baby shows all of the signs of growing well and is not forced to eat when not hungry. Feeding babies isn’t just about the numbers.

Table: Rough guide for daily milk intake by a baby at different ages



U.S. fluid ounces

Day 1



Day 3



Day 8



2 weeks



1-6 months



6-12 months



1-3 years



If you have a low milk supply and are using before-and-after weights to see how much milk you are making, how much milk a slow-growing baby is taking in, or if herbs or medications are increasing your milk supply, you should measure every breastfeed for at least one 24-hour period. Two 24-hour periods is ideal. Your results may look like those in the table below.

If you are using before-and-after weights to see if your premature baby is learning to breastfeed, you can just do weights for a number of feeds.  

B) Example of before-and-after weights showing that a baby is not taking in enough milk

One day of before-and-after weights by a mother without enough breast milk.

The table above was created by a mother breastfeeding a six-week-old boy. The mother had insufficient glandular tissue, so she did not have a full milk supply. The baby was able to latch, suck, and breastfeed normally

He was consistently hungry after breastfeeding and had lost too much weight (13% below birth weight) at Day 4, when infant formula supplements were started because the mother could only express small amounts of milk after breastfeeding.

At six weeks after birth, the baby was growing well, was contented, and his supplements had stabilized. His mother wanted to know how much milk her baby was taking from the breast and chose to use before-and-after weights to assess this.

C) Conversion

1) Grams to millilitres

1 gram (gm) of weight gain = 1 millilitre (ml) of milk

One ml of milk results in roughly one gram of weight gain. (The density of human milk is 1.031g/ml.) (Neville 1988).

Therefore, if a baby gains 30 gm, the baby has taken in 30 ml of milk.

2) Millilitres to U.S. fluid ounces

30 ml of milk equals roughly 1 U.S. fluid ounce (oz).

The actual conversion is 29.6 ml equals 1 oz.

D) Making the table

Steps to completing the table:

1) For column A, weigh the baby just before breastfeeding

2) For column B, weigh the baby right after breastfeeding 

3) For column C, calculate the amount of milk taken from the breast at one feed  

C = End weight – starting weight 

For example: at the 1 a.m. feed: 5,194 – 5,150 = 44 

4) For column D, the amount of supplement depends on the baby’s hunger signs. For example: at the 1 a.m. feed, the baby needed 30 ml (1 oz) to be contented

5) For column E, calculate the total amount of milk the baby receives at one feed

E = the amount of milk taken from the breast + the amount of supplement

For example: at the 1 a.m. feed: 44 + 30 = 74

6) For the totals at the bottom of the table, add the numbers in the columns above.

E) Information from the table

The table shows that on this day:

1) The baby’s before-weight was different for each weighing.

This is normal as the baby’s weight changed with:

  • The timing of pees
  • The timing of poops
  • The changes in the baby’s clothing

2) The baby always needed a milk supplement after breastfeeding to be happy.

Babies whose mothers have a low milk supply generally need a milk supplement after breastfeeding. Once they have been given enough milk, they are happy when held.

3) The amount of milk the baby gets from the breast and needs by supplement varies at each feed.

Each breastfeeding session is a little different. At each feed, this baby took in a range of:

  • Breast milk: 14 ml (1/2 oz) to 66 ml (2 oz)
  • Supplement: 15 ml (1/2 oz) ml to 75 ml (2 1/2 oz)

This is why 24 hours of before-and-after weights is more accurate than just doing it once or twice.

4) The baby had a typical number of feeds in one day.

A typical baby who is supplemented would need 6 to 8 breastfeeds a day. This baby had 8 feeds on this day.

5) The amount of breast milk the baby got through breastfeeding in one day is low.

By adding the amount of breast milk the baby takes at each feed, mothers can see how much milk the baby gets in 24 hours. This baby took in 326 ml (11 oz) on the first day.

The baby is six weeks old and needs about 800 ml (27 oz) of milk each day. The amount of breast milk he took in is a little less than half of the estimated total milk he needs.

F) Information from comparing two days of before-and-after weights

The mother completed a second 24 hours or before-and-after weights. The total amounts are in the table below. 

Table: Before-and-After Weights by a Mother Without Enough Breast Milk (First and Second Day)

1) The total amount of milk the baby takes in each day varies

On the first day, this baby took in a total of 696 ml (23 oz). On the second day, he took in a total of 772 ml (26 oz).

2) The total amount of milk the baby takes in is reasonable given the baby is growing well

Both numbers are less than the “average” of 800 ml (27 oz). The exact amount of milk taken each day is not as important as the other signs of normal growth.

In this example, the supplements were essential but did not need to be increased. Our clinic recommended that the mother continue to give the baby as much supplement as the baby needed to settle the hunger signs and be generally happy when fed and held.

3) The amount of breast milk that the mother makes is low.

This mother made 326 ml (11 oz) on Day 1 and 367 ml (12 oz) on Day 2. The amount varied a little but overall is low.

As this mother had insufficient glandular tissue, her milk supply was permanently low and the baby needed long-term infant formula supplements. This amount is actually on the higher side for a mother with this condition.


Neville MC, Keller R, Seacat J, et al. Studies in human lactation: milk volumes in lactating women during the onset of lactation and full lactation. Am J Clin Nutr. 1988 Dec;48(6):1375-86