Fluid Ounces to mL

Packing Liquids for a Cabin Bag Policed in Millilitres

Your shampoo is stamped 3.4 fl oz, the sunscreen beside it says 4 fl oz, and the sign above the security queue mentions only 100 mL. Almost nothing on a drugstore shelf in the United States is labelled in the unit the checkpoint actually enforces, so the pile on the bed has to be translated bottle by bottle before any of it goes into the wash bag.

Getting it wrong costs you the bottle. Screeners do not judge how much is left inside; the printed capacity on the container is what counts, so a 4 fl oz tube is 118.29 mL whether it is full or almost finished. That puts it 18 mL past a limit nobody at the belt has the authority to bend.

Conversion factor: 1 US fluid ounce = 29.5735295625 mL, so multiply fluid ounces by 29.5735. That makes 3.4 fl oz = 100.55 mL, while 100 mL comes back as 3.3814 fl oz — which is exactly why the two figures printed on the same notice never look equal.

Why the Limit Is Written as 100 mL

The metric figure came first

The restriction was agreed internationally in round metric terms, then translated for American travellers. 3.4 oz is the rounded English rendering of 100 mL, not a separate allowance.

Retail sizes that sit just over the line

Travel ranges cluster at 3, 3.4 and 4 fl oz. The first two clear the ceiling; the third works out at 118.29 mL and gets pulled from the tray every time.

Two ounces wearing one name

A British-labelled product quoting fluid ounces means 28.4130625 mL apiece, so its "3.5 fl oz" is 99.45 mL and legal, while an American 3.5 fl oz would be 103.51 mL.

The pouch has a ceiling of its own

Clearing 100 mL per bottle is only half the test. Everything still has to shut inside one small transparent bag, and ten compliant bottles will not fit in it.

Checking Every Bottle Before It Goes in the Wash Bag

Line the containers up on a table, read the capacity off each label, and run them through one after another. It takes a couple of minutes and it is far cheaper than replacing a moisturiser airside.

Type the capacity printed on the label

Put the fluid-ounce figure in the left field. Decimals accept a comma or a dot, so 3,4 and 3.4 read the same, and stray spaces are thrown away.

Watch the millilitre figure land

The right field refreshes on every keystroke, with no button to press. Anything that resolves above 100 goes in the hold bag; anything at or under it can travel in the cabin pouch.

Turn the question around for metric stock

Both boxes accept input, so a 75 mL tube typed on the right shows its ounce equivalent on the left. The swap button (↔) flips the pair for good when you are working through European packaging.

Copy the figure into your packing note

Each field has a copy button that hands over the digits alone, with no unit and no spacing, ready for the checklist you keep on your phone. Ctrl + C inside the field behaves identically.

Decant into a marked bottle, not a blank one. A refillable container with no capacity moulded into it gives the officer nothing to read, and the usual outcome is that it stays behind. Buy empties that show their size.

Cabin Liquid Rules and the Toiletry Sizes You Already Own

The per-container ceiling is the same round metric number nearly everywhere; what differs between authorities is the pouch, the wording and how the exemptions are handled. Check the departing airport's own page before you fly, because local arrangements change.

Authority or situation	Container ceiling	Same in US fl oz	Pouch rule and notes
TSA, United States	100 mL	3.38 fl oz	One quart-sized bag, roughly 946 mL, one per traveller — the "3-1-1" wording
United Kingdom and EU airports	100 mL	3.38 fl oz	One transparent resealable bag holding no more than 1 L, about 20 × 20 cm
CATSA, Canada	100 mL	3.38 fl oz	One clear 1 L bag; the same ceiling applies on domestic sectors
Australia and New Zealand	100 mL	3.38 fl oz	One 1 L bag, enforced on international departures
Duty-free bought after security	no set ceiling	—	Must stay in the sealed tamper-evident bag with the receipt showing through it
Medicine, baby milk, special diet	reasonable quantity	—	Declare it at the checkpoint; expect separate screening, opening or tasting
Toiletries in the hold	no volume ceiling	—	Spirits above 70% alcohol are barred; 24–70% is typically capped near 5 L per traveller

A handful of airports have trialled scanners that let passengers keep larger containers and stop unpacking the pouch altogether. The rollout has been uneven and the old ceiling has been reinstated at short notice more than once, so pack to 100 mL and treat any relaxation you meet on the day as a bonus.

What Helps While You Sort the Pouch

One bottle after another, nothing to reset

Type over the previous figure for each container in turn and the answer refreshes straight away, so a shelf of eight products takes under a minute to clear.

Reads metric packaging just as happily

Because both fields take input and the ↔ button reverses the pair, a 150 mL European bottle turns into ounces without touching anything else on the page.

Every volume unit in one searchable list

The dropdowns on both sides hold all 28 volume units, so the same page also sizes the litre pouch itself or turns a US quart bag into millilitres.

Plain numbers for a packing list

The copy button on each field gives the digits with nothing attached, which is what a notes app or a shared trip spreadsheet expects.

Questions at the Security Tray

Is 3.4 fl oz exactly the same as 100 mL?

No, and the gap runs the awkward way. At 29.5735295625 mL per US fluid ounce, 3.4 fl oz works out at 100.55 mL, fractionally over. Rounded honestly, 100 mL is 3.3814 fl oz. In practice a manufacturer who prints "3.4 fl oz / 100 mL" has filled to the metric figure and rounded the ounce number up for the label, so the bottle genuinely holds 100 mL. The figure that matters at the belt is the metric one beside it.

My bottle is only a third full — can I bring it anyway?

No. The restriction caps the size of the container, not the amount of liquid sitting in it. A 200 mL bottle with 60 mL left is still a 200 mL bottle and will be taken off you. There is no practical way for an officer to verify a fill level in a moving queue, which is why printed capacity is the whole test. Decant what you need into a marked travel bottle of 100 mL or less and leave the big one at home.

Are the fluid ounces on a British product the same as mine?

They are smaller. The imperial fluid ounce measures 28.4130625 mL against the American 29.5735295625 mL, a difference of about 4%. A UK-labelled 3.5 fl oz bottle is therefore 99.45 mL and passes, while the same figure on an American label means 103.51 mL and does not. Modern British packaging almost always shows millilitres as the primary size, so when both appear, read the metric one and ignore the ounce figure entirely.

What happens to a duty-free bottle bought after security?

A litre of spirits or a large perfume sold airside is exempt from the usual ceiling as long as it stays inside the sealed tamper-evident bag it was handed to you in, with the receipt visible through the plastic. Do not open that bag before you land. The catch is connections: some countries re-screen transfer passengers and will only accept a seal they recognise, so if your route changes airport or region, ask at the till before you buy.

Do prescription medicines and baby formula have to fit the pouch?

They do not. Liquid medication, and milk or food for an infant travelling with you, are permitted in quantities reasonable for the journey and sit outside the transparent bag. The trade-off is extra attention: take them out and declare them, expect containers to be opened or tested, and carry supporting paperwork such as a pharmacy label or a doctor's letter for anything unusual. Allow a few extra minutes at the checkpoint.