How the formula calculator works
A widely used guide for healthy, full-term babies who are only having formula is about 150 ml of formula per kilogram of body weight per day — roughly 2.5 oz per pound. The calculator multiplies your baby’s weight by this amount, caps the total at about 32 oz (950 ml), and divides it by a typical number of feeds for your baby’s age to estimate the size of each bottle.
Daily formula ≈ weight in kg × 150 ml (or weight in lb × 2.5 oz)
Example: a 5 kg baby needs about 750 ml a day. At 6–8 feeds, that is roughly 95–125 ml per feed.
Typical feeds by age
| Age | Feeds in 24 hours | Typical amount per feed |
|---|---|---|
| First week | 8–12 | Starts at 15–30 ml (½–1 oz), increasing day by day |
| 1–4 weeks | 8–12 | 60–90 ml (2–3 oz) |
| 1–2 months | 7–9 | 90–120 ml (3–4 oz) |
| 2–4 months | 6–8 | 120–180 ml (4–6 oz) |
| 4–6 months | 5–6 | 150–210 ml (5–7 oz) |
| 6–12 months | 4–5, plus solid food | 180–240 ml (6–8 oz) |
These are averages. Babies have growth spurts and hungrier days, and many take different amounts at different feeds.
Responsive feeding
Numbers are only a starting point. Watch your baby rather than the bottle: early hunger cues include stirring, rooting and sucking on hands; signs of fullness include slowing down, turning away and relaxing the hands. Hold your baby close, keep the bottle fairly horizontal so they can pace the feed, and never force them to finish a bottle.
Making formula safely
- Follow the instructions on the pack exactly — too much or too little powder can be harmful.
- Use the scoop that comes with the formula and level it off.
- Make each feed fresh where possible and throw away leftover formula after a feed.
- Clean and sterilise bottles as advised by your health service.
If your baby has reflux, allergies, was born early or is not gaining weight well, their needs may be different — follow the advice of your doctor, health visitor or dietitian. To track growth, use the Baby Growth Percentile Calculator.