Need a different amount? Use the millilitres to fluid ounces converter or go the other way with fluid ounces to millilitres.
Where 3.38 comes from
A US fluid ounce is defined as exactly 29.5735295625 ml (NIST). Divide 100 by that and you get 3.3814, so 3.38 US fl oz. The TSA rounds up to 3.4 oz. Going back the other way, 3.4 US fl oz × 29.5735 ≈ 100.55 ml, which is close enough that the two labels describe the same travel-size bottle.
The UK imperial fluid ounce is a bit smaller: 28.4130625 ml (Weights and Measures Act 1985). That makes 100 ml ≈ 3.52 imperial fl oz. You'll rarely see imperial fluid ounces on toiletries, but it's why the "oz" figure on an older British bottle might not match a US one.
Watch out for "oz" meaning weight. On a jar of cream or a tube of toothpaste, "oz" may be an ounce of weight (28.349523125 g). 100 g is about 3.53 oz by weight. The grams to ounces converter handles that one.
| Millilitres | US fl oz | Imperial fl oz |
|---|---|---|
| 50 ml | 1.69 | 1.76 |
| 100 ml | 3.38 | 3.52 |
| 250 ml | 8.45 | 8.80 |
| 1,000 ml (1 litre) | 33.81 | 35.20 |
(Aorista's calculations from the NIST and UK definitions above.)
The rule is about the container, not what's left in it
This catches a lot of people. In New Zealand, Australia and the UK, the official guidance is clear that the limit is the size of the container:
- New Zealand: "This restriction applies to the size of the container and not its content." A 150 ml bottle with 50 ml left in it is still prohibited (Aviation Security Service).
- Australia: "You cannot take containers larger than 100 mL or 100 g, even if they are only partially-filled." The example given is a half-full 200 g toothpaste tube (Department of Home Affairs).
- UK: at most airports you can't take containers larger than 100 ml through security, and "this still applies if the container is only part full" (GOV.UK).
The TSA's wording also limits items to "travel-sized containers that are 3.4 ounces (100 milliliters) or less per item".
If a label shows both ml and g, New Zealand's rule is to use the millilitres. Grams are only used when no millilitre figure is given (Aviation Security Service).
Bag size: "quart-sized" vs "20 × 20 cm"
Every country here asks for your small containers to go in one clear bag, but each describes it differently:
| Where you're flying from | What the official source says |
|---|---|
| United States | "a quart-sized bag" of liquids, aerosols, gels, creams and pastes (TSA). A US quart is about 946 ml (NIST). |
| New Zealand (international flights) | containers must not exceed one volumetric litre in total, presented in "a single re-sealable 20cm by 20cm" plastic bag (Aviation Security Service) |
| Australia (international flights) | one transparent, re-sealable bag whose four sealed sides add up to no more than 80 cm, for example 20 × 20 cm or 15 × 25 cm; one bag per passenger (Home Affairs) |
| United Kingdom | if the airport asks for a bag, it's one transparent resealable bag holding no more than a litre, about 20 × 20 cm, one per person. Not every UK airport requires this (GOV.UK). |
A standard 20 × 20 cm snap-lock bag should satisfy all four descriptions. If you're unsure, check the airport you're departing from.
Country notes worth knowing
New Zealand. The liquid limits apply to carry-on luggage on international flights only. They don't apply to domestic flights or checked luggage (Aviation Security Service). At Auckland Airport, since 1 May 2024, international passengers no longer have to take 100 ml-or-under liquids out of their bag for screening (Auckland Airport). The 100 ml container limit still applies.
Australia. The restrictions apply when departing Australia on international flights and when transiting through Australia. They "do not apply to your checked baggage or most domestic flights". Aerosols need a fitted cap or locking device (Home Affairs).
United Kingdom. The rules "depend on the airport". GOV.UK says some airports may allow containers up to 2 litres, and you should check the rules at the airport you're flying from, at any airport you transit, and on your return journey. Just because your outbound UK airport allows larger containers, don't assume your connection or return flight will (GOV.UK).
United States. Liquids in containers larger than 3.4 oz (100 ml) go in checked baggage, and anything that alarms during screening gets extra screening (TSA).
Powders have their own limit
Both New Zealand and Australia limit inorganic powders (salt, sand, some talcum powders and powdered deodorants) to 350 ml or 350 g per person in your carry-on. Organic powders like coffee, protein powder and baby formula aren't restricted in Australia. In New Zealand, inorganic powders don't need to go in the plastic bag (Aviation Security Service; Home Affairs).
Medicines, baby food and duty free
- Medicines and infant food are exemptions under the TSA rule.
- In the UK, you can take containers up to 2 litres through security at all airports if they're for essential medical purposes, special dietary requirements, or baby food and milk (GOV.UK). You need proof of prescription for liquid medicine in containers over 100 ml.
- New Zealand allows prescribed medicines above the limits if the prescription is in your name and in its original packaging. You can bring the amount you need for the flight (Aviation Security Service).
- Duty free: the TSA allows duty-free liquids over 3.4 oz on a connecting flight into the US if they're in a tamper-evident bag with the original receipt and bought within 48 hours. Australia and the UK also require the sealed bag with proof of purchase. New Zealand's guidance says to check what you need to do at each airport you'll travel through.
A simple way to pack
- Check each bottle's printed size, not how full it is.
- Fit everything into one clear 20 × 20 cm resealable bag.
- If you have a connection, check the rules at the transit airport too.
- Put anything bigger in your checked bag.
Our packing lists for a weekend getaway and a business trip let you tick off toiletries as you go. If you're heading to the United States or the United Kingdom, their country pages collect the other travel essentials in one place.
Rules change and screening officers have the final say. Check the official page for each airport on your trip before you fly.
Quick answers
Is 3.4 oz the same as 100 ml?
Close enough for airport purposes. 100 ml is 3.38 US fl oz, and the TSA writes the limit as "3.4 ounces (100 milliliters)".
Can I take a 150 ml bottle if it's only half full?
Not in New Zealand, Australia or at most UK airports. The limit is the container size, even if it's partly empty.
Do the liquid rules apply on domestic flights in New Zealand?
No. New Zealand's Aviation Security Service says they apply only to carry-on luggage on international flights.
Do I need to take my liquids out at Auckland Airport?
Not for international flights since 1 May 2024, according to Auckland Airport. Your containers still need to be 100 ml or less and fit in one 20 × 20 cm bag.
Are all UK airports still limited to 100 ml?
GOV.UK says the rules depend on the airport. Most still limit containers to 100 ml, but some allow up to 2 litres. Check your departure, transit and return airports.
How big is a quart-sized bag in centimetres?
The TSA doesn't give dimensions. A US quart is about 946 ml (NIST), roughly the one-litre capacity that New Zealand and the UK describe as a 20 × 20 cm bag.
Sources
- TSA, "Liquids, Aerosols, and Gels Rule": https://www.tsa.gov/travel/security-screening/liquids-aerosols-gels-rule. Covers 3.4 oz (100 ml), the quart-sized bag, exemptions, and duty free (48 h, tamper-evident bag, receipt).
- NIST, Handbook 44 Appendix C / SI conversion (1 US fl oz = 29.5735295625 ml; 1 US qt = 0.946352946 L): https://www.nist.gov/pml/owm/approximate-conversions-us-customary-measures-metric
- UK Weights and Measures Act 1985, Schedule 1 (1 fl oz = 28.4130625 ml): https://www.legislation.gov.uk/ukpga/1985/72/schedule/1
- International avoirdupois ounce = 28.349523125 g (NIST, as #2).
- Aviation Security Service (NZ), "Powders, liquids, aerosols, and gels (PLAGs)": https://www.aviation.govt.nz/passenger-information/powders-liquids-aerosols-and-gels-plags/. Covers container size not content, ml over g, the 20 × 20 cm bag of one volumetric litre, international only, 350 ml powders, medicine, and duty free.
- Auckland Airport, "The Restrictions Explained": https://www.aucklandairport.co.nz/information/departure-information/the-restrictions-explained. Liquids no longer need to be removed for screening from 1 May 2024 (international).
- Australian Department of Home Affairs, "What you can and can't bring" (last updated 28/09/2026): https://www.homeaffairs.gov.au/about-us/what-we-do/travelsecure/security-screening-at-airports/what-you-can-and-cant-bring. Covers 100 mL/100 g, the 80 cm bag, one per passenger, partly filled containers, aerosol caps, and 350 mL/g inorganic powders.
- GOV.UK, "Hand luggage restrictions at UK airports", Liquids, Medicines and Baby food parts (updated 1 Oct 2026): https://www.gov.uk/hand-luggage-restrictions/liquids. Covers airport-dependent rules, part-full containers, up to 2 L at some airports, the 2 L exemptions at all UK airports, and the duty-free security bag.
Related: All travel guides