About the Breast Milk Calculator
This breast milk calculator tells you how much expressed milk to put in each bottle and how much to leave with a caregiver while you are away. Exclusively breastfed babies drink a remarkably steady amount between 1 and 6 months — about 25 fl oz (750 mL) a day on average, with a normal range of roughly 19–30 oz — so the per-bottle amount mostly depends on how many times a day your baby feeds.
It is designed for pumping parents returning to work, partners and grandparents giving occasional bottles, and anyone building a freezer stash. Enter your baby’s age band (or your own measured daily intake) and the number of feeds in 24 hours, then the hours you will be apart, to see how many bottles and ounces to prepare.
Unlike formula, breast milk intake does not keep rising with weight after the first month, which is why bottles are often smaller than formula guides suggest. The figures are averages — some babies take more or less — so start with the suggested amount, offer small top-up bottles of 1–2 oz rather than large ones, and follow your baby’s cues.
With the default inputs, the milk per bottle is 3.1 fl oz. Change any value above to recalculate instantly.
How to use the breast milk calculator
- 1Pick your baby’s age band, or choose your own daily amount if you have measured it.
- 2Enter how many times your baby feeds in 24 hours, including at night.
- 3Enter how many hours you will be apart from your baby.
- 4Read the amount per bottle and the total milk to leave with your caregiver.
- 5Pack an extra small bottle and adjust over a few days based on what baby actually drinks.
Formula and method
The daily intake comes from the age band you choose: about 16 oz in the first week, 22 oz in weeks 1–4, a plateau of about 25 oz from 1 to 6 months, and slightly less (about 23 then 21 oz) once solids are established. You can replace it with your own measured daily amount.
Dividing the daily amount by the number of feeds in 24 hours gives the amount per bottle. The number of bottles to leave is the hours apart multiplied by feeds per hour, rounded up to a whole bottle, and the milk to leave is that number of bottles times the per-bottle amount. Millilitres use 29.57 mL per fl oz.
- D
- Daily breast milk intake (fl oz)
- F
- Feeds per 24 hours
- H
- Hours apart from baby
- B
- Bottles to leave = ⌈H × F ÷ 24⌉
Worked examples
3-month-old, 8 feeds, 9-hour work day
At 25 oz a day over 8 feeds, each bottle holds about 3.1 oz (92 mL). Feeds come roughly every 3 hours, so a 9-hour separation needs 3 bottles — about 9.4 oz of milk in total.
2-week-old feeding 10 times a day
A baby in weeks 1–4 takes about 22 oz a day; over 10 feeds that is 2.2 oz (65 mL) per bottle. Four hours apart at one feed every 2.4 hours rounds up to 2 bottles, or 4.4 oz.
Measured 30 oz a day, 6 feeds, 10 hours apart
With a known intake of 30 oz over 6 feeds, bottles are 5 oz each. Ten hours at one feed every 4 hours is 2.5 feeds, rounded up to 3 bottles — 15 oz (about 444 mL) of milk.
Frequently asked questions
How much breast milk should I put in a bottle?+
Divide your baby’s daily intake by the number of feeds. Between 1 and 6 months most breastfed babies take about 25 oz a day, so with 8 feeds a bottle is about 3 oz and with 10 feeds about 2.5 oz.
Why do breastfed babies drink less per bottle than formula-fed babies?+
Breast milk intake plateaus at around 25 oz a day from 1 to 6 months, while formula guidelines scale with weight. Breast milk composition also changes as babies grow, so volume does not need to keep rising.
How much milk should I leave for daycare?+
Estimate one bottle for every feed your baby would normally have while you are apart, using the per-bottle amount, then add a small 1–2 oz backup. Many parents leave 1–1.5 oz per hour of separation.
How long can pumped breast milk be kept?+
CDC guidance: freshly expressed milk can stay at room temperature up to 4 hours, in the refrigerator up to 4 days, and in the freezer about 6 months (up to 12 months is acceptable). Thawed milk should be used within 24 hours.
Does my baby need more breast milk as they get bigger?+
Not usually between 1 and 6 months — intake stays fairly steady. After about 6 months, solid foods start to supply some calories and milk intake typically decreases gradually through the first year.
This tool gives general estimates and is not medical advice. Talk to a doctor or qualified professional about your health, diet or training.