Oz to mL Baby Formula — 2, 3, 4 and 6 Ounces

One US fluid ounce is 29.5735 mL, so a 4 oz bottle holds about 118 mL and a 6 oz bottle about 177 mL. Enter either unit:

Bottle sizes, converted

Fluid ounces	Exact mL	Usually printed as
1 fl oz	29.6 mL	30 mL
2 fl oz	59.1 mL	60 mL
3 fl oz	88.7 mL	90 mL
4 fl oz	118.3 mL	120 mL
5 fl oz	147.9 mL	150 mL
6 fl oz	177.4 mL	180 mL
8 fl oz	236.6 mL	240 mL

Both columns are on your bottle, and they disagree slightly at every line. That is not a manufacturing fault: the ounce ladder climbs in steps of 29.57 mL while the metric ladder climbs in steps of 30, so by 8 oz they are more than 3 mL apart. Read one scale and stay on it.

The number that actually governs the bottle

Here is the thing this conversion cannot tell you: volume is not the recipe. Powdered infant formula is mixed by a fixed ratio, and the AAP states it as one level unpacked scoop of powder to 2 ounces of water — using the scoop that came in that can, because scoops differ between brands.

That ratio is what determines whether the feed is correct, and it is expressed per two ounces precisely so you never have to convert anything. Four ounces of water takes two scoops. Six ounces takes three. There is no step at which the millilitre figure enters.

Concentrated liquid formula is mixed one to one with water. Ready-to-feed takes no water at all — adding any turns it into diluted formula.

Why thinning formula is dangerous

The AAP’s warning on this is unusually direct: formula with too much water added does not contain enough of the nutrients babies need, which can slow their growth and development, and diluting it disturbs the balance of sodium, potassium and calcium badly enough to cause seizures.

An infant’s kidneys cannot clear a large water load, so extra water is not neutral the way it is for an adult. This is why babies in the first six months are not given plain water either, unless a pediatrician says otherwise.

The everyday version of this risk is not deliberate. It is measuring the water after adding the powder rather than before, or topping the bottle up to a line, or using a different can’s scoop. All three change the ratio without looking like a change.

Practical rules for the 3 a.m. bottle

• Water first, then powder. Fill to the water line, then add scoops. Powder displaces volume, so measuring after mixing gives less water than the recipe.
• Level, unpacked scoops. Not heaped, not tapped down.
• One brand’s scoop for one brand’s can.
• Follow the label. If the can’s directions differ from a general rule, the can wins.

For the other conversion new parents meet in the same week — the weight the maternity ward gave you in pounds and ounces — see baby weight to kg. And for medicine measured in drops rather than ounces, drops to mL.

This content is informational. Preparation and volumes for infant formula should follow the product label and your pediatrician’s advice.