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MasterMath

Baby Formula Calculator

A 4.2-kilo baby needs about 630 ml a day, which across seven feeds is 90 ml a bottle. Work out the amount per feed from weight and age.

Per feed

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Per feed—
Per day—
Rule applied—
One feed every—
If formula, per bottle—

How this was worked out

    Indicative result. These amounts are for infant formula. Breastfeeding on demand is not measured: the baby regulates the amount, and what is watched is weight gain and wet nappies. If you are unsure whether they are feeding enough, ask your health visitor or paediatrician.

    The formula

    ml per day = weight in kg × 150 · per feed = ml per day ÷ number of feeds

    Where it comes from

    The rule of 150 millilitres per kilo per day holds from the first week to six months, when solids start and the volume stops growing. It does not apply before the first week: a newborn's stomach on day one is the size of a cherry and takes about 60 millilitres per kilo, rising in steps to 150 by around day six.

    How to work it out by hand

    1. Multiply the weight in kilos by 150
    2. That is the total for the day in millilitres
    3. Divide by the number of feeds
    4. To make it up, one level scoop per 30 ml of water

    What is worth knowing

    The water goes in first and the powder after, not the other way round: the scoop dissolves into the water, which is why the ratio is per 30 millilitres of water and not of the finished bottle. A baby who leaves some behind is almost always fine: the figure is an average and appetite changes between feeds and between days. What is worth watching is the trend in weight and the nappies, not what is left in one particular bottle.

    Frequently asked questions

    How much milk does a one-month-old take?

    About 150 ml per kilo per day. At 4 kilos that is 600 ml, across six or seven feeds.

    How many scoops per bottle?

    One level scoop per 30 ml of water. For 120 ml, four scoops.

    What if they are breastfed?

    It is not measured. Breastfeeding is on demand and the baby adjusts the amount themselves.

    What if they leave milk?

    Nothing, as long as they are gaining weight normally. The figure is an average, not a quota to finish.