Can I bring a 4 oz bottle on a plane if it's not full?

For an ordinary liquid under the standard US carry-on rule, a partly filled 4 US fluid-ounce bottle (about 118 ml capacity) is too large. The amount left inside does not reduce the container’s capacity. TSA limits ordinary carry-on liquid containers to 3.4 fluid ounces (100 ml). Medical, nourishment and qualifying duty-free exemptions are separate cases described below. This answer concerns a partly filled liquid container; it is not a statement that an empty bottle is prohibited. Check the exact item and screening instructions. TSA liquids rule.

What the 3-1-1 rule actually limits

• Per container: Each liquid, aerosol, gel, cream or paste must be in a container of 3.4 oz (100 ml) or less (TSA liquids rule).
• One bag: All those containers must fit comfortably in a single quart-size, clear, zip-top bag, one bag per passenger (TSA travel checklist).
• Screening: In standard screening, remove your 3-1-1 bag and place it in a bin (TSA travel checklist).

What to do with a 4 oz bottle

• Decant: Transfer what you need into a clearly sized 3.4 oz (100 ml) or smaller travel bottle, then place it in your quart bag.
• Check it: Put the original 4 oz container in checked luggage.
• Mail or leave it: If you brought it to the checkpoint, you can exit to check it or discard it to proceed.
• Buy after security: Purchase toiletries airside if you prefer not to decant.

Note: Duty-free liquids over 3.4 oz may be permitted when purchased internationally and carried in a secure, tamper-evident bag on inbound itineraries with a U.S. connection, with the original receipt and no signs of tampering. Keep the original receipt showing purchase within 48 hours, and these items must still clear screening, and anything that alarms or cannot be screened will not be allowed (TSA liquids rule). This exception applies to qualifying duty-free purchases, not ordinary toiletry bottles you brought from home.

Quick example

A half-full 4 oz shampoo bottle still exceeds the container limit and will be refused in your carry-on. Pour it into a 100 ml-capacity travel bottle and place it in your quart bag, or pack the 4 oz bottle in your checked bag (TSA liquids rule).

Allowed exceptions that can exceed 3.4 oz

• Medications: TSA lists medications as an exemption. Expect additional screening if needed (TSA liquids rule).
• Infant and child nourishments: Formula, breast milk and similar nourishments are also listed as exemptions and may undergo extra screening (TSA liquids rule).

Put this into practice

Read each container’s labelled capacity before filling the clear pouch. The amount left inside does not change the size of a 4 US fl oz container, and exceptions need their own applicable screening process.

Carry-on liquids quick check

• Confirm every ordinary liquid container is 3.4 oz (100 ml) or less
• Fit ordinary liquid containers in one quart-size, clear zip-top bag
• Place your 3-1-1 bag in a bin during standard screening
• Move any larger containers to checked baggage
• Keep exempt items (medications, infant nourishments) separate and be ready for additional screening

FAQ

Does squeezing air out or carrying a half-full 4 oz bottle make it OK?
No. TSA limits the container size itself to 3.4 oz/100 ml or less. Larger containers must be checked (TSA liquids rule).

Do I really need to take the quart bag out?
In standard screening lanes, yes: remove your 3-1-1 bag and place it in a bin for X-ray screening (TSA travel checklist).

Related reading

• Does toothpaste count as a liquid for carry-ons? A practical guide
• How to wash out travel bottles (and keep your toiletry bag clean)