Baby Formula Calculator
Estimate how much formula milk a bottle-fed baby needs per day and per feed from their weight, using the NHS 150–200 ml per kg per day guideline — with pounds supported for US and Australian tins.
Estimated formula per day
600–800 ml/day
- Per feed (over 6 feeds)
- 100–135 ml
- In fluid ounces
- 20.3–27.1 fl oz/day
- Guideline used
- 150–200 ml per kg per day
- Weight
- 4.00 kg
Using the NHS guide of 150–200 ml of formula per kilogram of body weight per day, a 4.00 kg baby needs about 600–800 ml/day, split into 6 feeds of roughly 100–135 ml. Babies self-regulate from feed to feed, so treat this as a starting point: follow their hunger and fullness cues and the instructions on your formula tin, and speak to your health visitor, midwife or doctor about your own baby. This tool is informational and is not medical advice.
How to use this calculator
Choose whether you're entering your baby's weight in kilograms or pounds, type the current weight, and set how many feeds you split the day into — six is a common starting point, though many newborns take eight or more smaller feeds. The headline result is the estimated formula for a whole day, shown as a range; the breakdown converts that into the amount per bottle, the same figure in US fluid ounces, and the guideline the numbers come from. If you only know your baby's weight in pounds and ounces, convert the ounces to a decimal first (a pound is 16 ounces, so 8 lb 8 oz is 8.5 lb). The guide covers formula-fed babies from the end of the first week to around six months, before solid foods begin to replace some milk.
How the calculation works
The calculation follows the NHS rule of thumb that, from the end of the first week until around six months, a formula-fed baby needs roughly 150 to 200 millilitres of made-up formula per kilogram of body weight per day. Multiply the weight in kilograms by 150 for the lower end of the range and by 200 for the upper end, then divide by the number of feeds to get the amount per bottle. Pounds are converted at 1 lb = 0.45359 kg before the same maths is applied. The American Academy of Pediatrics expresses the same idea in imperial units — about 2.5 fluid ounces per pound per day, which works out to roughly 163 ml/kg and sits neatly inside the NHS band — and adds a practical ceiling of about 32 fluid ounces (around 945 ml) a day. This calculator applies that ceiling, so for heavier babies the daily total plateaus rather than climbing indefinitely: past that point, and from about six months, solid foods gradually take over rather than ever-larger bottles.
Worked example
A one-month-old weighing 4 kg: 4 × 150 = 600 ml at the lower end and 4 × 200 = 800 ml at the upper end, so about 600 to 800 ml across the day — exactly the figure the NHS uses in its own worked example. Divided into six feeds that is roughly 100 to 135 ml per bottle. In imperial terms, a 10 lb baby (about 4.54 kg) works out at roughly 680 to 910 ml a day; the AAP’s own rule of 2.5 oz per pound gives 25 fl oz (about 740 ml), which falls comfortably inside that range. A larger baby of 8 kg would in theory need 1,200 to 1,600 ml, but the calculator caps the result at about 945 ml — the point where most formula-fed babies level off and start moving toward solids.
Frequently asked questions
How much formula does my baby need per day?
As a general guide, the NHS suggests a formula-fed baby needs about 150 to 200 ml of made-up formula per kilogram of body weight per day from the end of the first week until around six months. So a 4 kg baby needs roughly 600 to 800 ml a day, and a 6 kg baby roughly 900 to 1,200 ml — though most babies plateau at around 32 fl oz (about 945 ml) a day. This is a starting estimate, not a target to hit exactly: healthy babies vary day to day and regulate their own intake. Always follow the make-up instructions on your specific formula tin, and check with your health visitor, midwife or doctor about your own baby.
How many ounces of formula should my baby drink?
The American Academy of Pediatrics rule of thumb is about 2.5 fluid ounces of formula per pound of body weight per day, up to a maximum of around 32 fl oz. So an 8 lb baby takes about 20 oz a day, a 10 lb baby about 25 oz, and a 12 lb baby about 30 oz — split across six to eight feeds. This calculator shows the daily estimate in both millilitres and fluid ounces so you can match whichever unit your bottles and formula tin use.
Why does the calculator give a range instead of one number?
Because babies are not machines. The NHS guidance is deliberately a band — 150 to 200 ml per kg per day — because appetite varies with growth spurts, illness, activity and simply the individual child. A baby who takes the lower end one day and the upper end the next is completely normal. Use the range as a sensible window rather than a precise dose, and let your baby’s hunger and fullness cues do the fine-tuning: a baby who is feeding well, has plenty of wet nappies and is growing along their line on the chart is getting enough.
Does this work for breastfed or combination-fed babies?
No — this guideline is specifically for babies fed only on infant formula. Breastfed babies feed on demand and there is no equivalent millilitre-per-kilogram figure, because the amount transferred at the breast is self-regulating and cannot be measured this way. If you combination feed, the formula portion of your baby’s intake will be lower than these numbers because breast milk makes up the rest, so treat the result as an upper reference only and be guided by your baby and your health visitor.
What if my baby wants more or less than the calculator says?
Small differences are normal and usually nothing to worry about — babies regulate their own intake, and forcing a baby to finish a bottle or holding one back to hit a number is not recommended. Persistently taking far more or far less than expected, poor weight gain, very few wet nappies, or signs of distress are worth discussing with a health professional. This tool gives a population-level estimate; your health visitor, midwife or doctor can weigh your baby, look at the trend over time and advise on your individual situation.
Is this calculator medical advice?
No. It is an informational tool that applies published NHS and AAP feeding guidelines to the weight you enter. It cannot see your baby, account for prematurity, medical conditions, reflux, allergies or a doctor’s specific instructions, and it should never override the make-up guidance on your formula tin or advice from a qualified health professional. If you have any concern about your baby’s feeding or growth, speak to your health visitor, midwife, pharmacist or doctor.