mL to Fluid Ounces

Bottles in Ounces, Logs in Millilitres

Bottle feeding runs on two scales at once. The bottle in your hand is usually moulded with ounce numbers down one side and millilitres down the other. The tin of formula gives its preparation instructions in scoops per ounce, or per 100 mL, depending on where it was made. The feeding app, the red book and the chart at a hospital weigh-in all record millilitres. Anyone tired enough to be doing a 3 a.m. feed deserves a straight answer about which number is which.

Conversion factor: 1 mL = 0.0338140227 US fl oz, and 1 US fl oz = 29.5735295625 mL. So a feed logged as 120 mL is 4.058 fl oz — the 4 oz line on the bottle, with a couple of millilitres to spare.

Where Each Scale Comes From

Two scales moulded into one bottle

Manufacturers print both because the same bottle is sold on both sides of the Atlantic. The ounce side steps in whole and half ounces; the millilitre side steps in 20, 25 or 30 mL, so the two ladders rarely meet on a line.

The tin sets the ratio

Preparation instructions are part of the product, not a general rule. Some tins are written as one level scoop per 2 fl oz of water, others per 30 mL or per 100 mL, and scoop sizes differ between brands and stages.

Records are kept in millilitres

Intake and output charts, health-visitor notes and feeding apps almost all use mL, because clinical intake is worked out per kilogram of body weight and the arithmetic only stays clean in metric.

The ounce has a rounded twin

The US customary fluid ounce is 29.5735295625 mL, but US nutrition labelling uses a rounded 30 mL. That is why some instructions say "per ounce" and others "per 30 mL" and both are describing the same scoop.

Reading One Feed in Both Scales

Most of the time you are translating in one direction only: a number someone else wrote down into the scale printed on the equipment in front of you.

Type the millilitre figure from the log or the tin

Enter 60, 120, 150 — whatever the chart, app or instruction sheet says — in the left field. The ounce value appears as you type, and a comma works just as well as a dot for decimals.

Match it to the nearest moulded line

Bottle graduations are coarse, so read to the nearest line rather than chasing decimals: 4.058 fl oz is simply the 4 oz mark. If the two scales disagree by a millimetre of liquid, follow the one your formula instructions are written in.

Copy the figure into the feed log

The copy button hands over the bare number with no unit attached — quick to paste into a tracking app, a shared note between parents, or a form for nursery. Ctrl + C in a field does the same.

Flip it when the numbers arrive in ounces

Press the swap button (↔) for fl oz → mL, the direction you need when a US tin, a relative or an American parenting site quotes ounces and the log you keep is metric. 5 fl oz comes back as 147.87 mL.

This is not feeding advice. This page converts units of volume. It does not say how much a baby should be fed, and no figure here is a recommendation. Follow the preparation instructions printed on your formula tin, and speak to your health visitor, midwife, paediatrician or pharmacist about feed amounts.

Typical Feed Volumes by Age, in Both Scales

Published guidance from the NHS, the American Academy of Pediatrics and Nemours KidsHealth describes broadly similar ranges. These are typical observed figures, not targets — babies of the same age genuinely differ, and what matters is the pattern over several days rather than any single feed. Ounce columns are converted from the millilitre ranges.

Age	Typical feed (mL)	Same feed (fl oz)	Feeds in 24 h	Typical daily total
First week	30–90 mL	1.01–3.04 fl oz	8–12	Rising steeply day by day
2–4 weeks	90–120 mL	3.04–4.06 fl oz	6–8	480–800 mL (16.2–27.1 fl oz)
About 2 months	120–150 mL	4.06–5.07 fl oz	5–6	720–900 mL (24.3–30.4 fl oz)
About 4 months	120–180 mL	4.06–6.09 fl oz	5–6	750–1,000 mL (25.4–33.8 fl oz)
About 6 months	180–230 mL	6.09–7.78 fl oz	4–5	750–1,000 mL (25.4–33.8 fl oz)

Two things stand out. First, the ounce figures are almost never round — a tidy 150 mL is an untidy 5.07 fl oz, which is exactly why a bottle's two scales look mismatched. Second, NHS guidance frames intake per kilogram of body weight, roughly 150–200 mL per kg per day for the first six months, and that calculation only works in metric. The ounce column is for reading the bottle; the millilitre column is for everything written down.

Handy Details for Feed-Time Arithmetic

One-handed and live

Both fields update as you type, so you can run through a whole day of feeds without clearing anything between them — useful when the other hand is holding a bottle.

Ounce-first instructions, metric log

The swap button turns the page into fl oz → mL for tins and advice written in ounces, so the figure you record stays in the units your notes use.

Daily totals, not just single feeds

Nothing caps the input, so a 24-hour total of 850 mL converts as readily as one 120 mL bottle — handy when a clinic asks for the day's intake in the other scale.

Straight into the tracking app

Copy gives the number alone, with no unit or spacing to strip out before it goes into a feeding app field or a shared note.

Questions About Bottles, Scoops and Feed Logs

How many millilitres does each ounce mark on a baby bottle represent?

29.5735295625 mL per US fluid ounce. So the 2 oz line sits at 59.15 mL, the 4 oz line at 118.29 mL, the 6 oz line at 177.44 mL and the 8 oz line at 236.59 mL. Formula instructions written in the US often simplify this to 30 mL an ounce, which is the rounded value used on nutrition labels — that is where the familiar "8 oz bottle = 240 mL" comes from, even though 8 fl oz is really 236.59 mL.

Why don't the two scales on my bottle line up with each other?

Because neither scale is a translation of the other — both are printed at their own round numbers. Ounces climb 1, 2, 3, 4; millilitres climb 30, 60, 90, 120. The two ladders only come close by accident, since 4 oz is truly 118.29 mL rather than 120 mL. Moulded graduations also carry manufacturing tolerance, and research on feeding bottles has found real variation in marking accuracy between products, so treat the lines as good guides rather than laboratory measurements.

My tin says one scoop per ounce and my bottle is marked in millilitres — can I mix the two systems?

No — pick the system your tin is written in and stay in it. Scoops are matched by the manufacturer to a specific water volume, and scoop size varies between brands and stages, so a scoop from one tin is not interchangeable with another. If the instructions are per ounce, measure the water in ounces; if they are per 30 mL or per 100 mL, measure in millilitres. Converting halfway through is how formula ends up too concentrated or too dilute. The tin's own instructions always win.

Is it a problem that 60 mL is not exactly 2 oz?

On a bottle scale, no. 60 mL is 2.029 fl oz — 0.85 mL more than a true 2 fl oz, about 1.4 %, or a fraction of a millimetre of liquid height in a feeding bottle. That is smaller than the difference between reading the meniscus from above and from eye level. The place to be exact is the powder-to-water ratio, not the conversion: measure the water to the line the tin's instructions describe, add the stated number of level scoops, and let the rounding go.

Why do hospitals and intake charts insist on millilitres?

Because everything clinical is calculated per kilogram. Intake is compared against body weight — NHS guidance describes roughly 150–200 mL per kg per day for babies under six months — and weights are recorded in kilograms, so a metric volume keeps the sum to a single division. Millilitres also match the syringes, feeding tubes and medicines used alongside. Ounces would add a conversion step to a calculation nobody wants to get wrong at speed.