How to Pack Liquids for a Flight

This page summarizes published TSA guidance. Rules differ outside the US, individual checkpoints vary, and a screening officer has the final say on any item. The authoritative source is linked at the bottom.

The rule, stated precisely

Three numbers, and each of them is misread in a specific way.

The per container point is the important one. A 3.4 oz bottle is legal whether it is full or a quarter full — but a 6 oz bottle containing 1 oz of shampoo is not, because the rule is about the container’s stated capacity, not its contents. That specific mistake is the commonest reason something gets binned at a checkpoint.

The bag is the real limit

A quart is 0.95 L. Once you account for the shape of the bottles and the air between them, you fit roughly six to nine containers of 3.4 oz in one — not the eleven the arithmetic suggests.

This is why buying a large toiletry bag does not help. The published 4.5 L hanging toiletry bag in our ledger is nearly five times the quart, which makes it an excellent bag for solids and checked travel and irrelevant to the liquids allowance. The toiletry bags compared.

The specification to match is the Peak Design Small Wash Pouch at a published 1 L — essentially quart-sized, which is the whole point of it.

What does not count against the bag

The most useful part of the rule and the least known. Several categories are exempt from the 3-1-1 limits, and taking advantage of them frees up most of the quart.

• Medically necessary liquids — prescription and over-the-counter medication, in reasonable quantities. Declare them at the checkpoint and they travel outside the bag. The medication rules in full.
• Baby formula, breast milk and baby food, in reasonable quantities, whether or not the child is traveling with you. Declare them.
• Duty-free liquids bought airside, in a sealed tamper-evident bag with the receipt inside.
• Ice packs for the above, where required to keep them cool.

Everything in that list still gets screened, sometimes separately, and the officer can ask questions. Declaring it up front turns a search into a conversation.

The best trick is not carrying liquids at all

Anything that is not a liquid, gel, aerosol, cream or paste is not covered by the rule at all, and there is a solid version of almost everything in a wash bag.

Swap those six and the quart bag holds only what genuinely has to be liquid — which for most people is a contact lens solution, a moisturizer and a small perfume. Note the deodorant row specifically: a solid stick is not a gel and does not go in the bag, while a roll-on or gel does.

Or check it

The 3-1-1 rule applies only to carry-on. A checked bag can hold full-size bottles with no volume limit for ordinary toiletries.

Two cautions if you do. Bottles leak at altitude, because the pressure inside them is higher than the pressure in the hold — so decant into containers with real seals and bag them. And a checked bag is a bag that can be delayed, so the medication and the contact lens solution stay with you regardless. Why that matters.

At the checkpoint

1. Take the bag out and put it in a tray unless the lane has a CT scanner and the signage says otherwise.
2. Keep it reachable — an outer pocket, not the middle of the main compartment. This is the difference between a two-second action and unpacking on a bench.
3. Declare medication and baby liquids before the bag goes through, not after it is pulled.
4. Water bottles must be empty. Every time, no exceptions. Fill it after. Which bottle, and why 0.95 L is a coincidence worth noticing.
5. Expect the rules to differ abroad. Many airports have moved to scanners that permit larger volumes; many have not, and some enforce more strictly than the US. Check the departure airport, not the destination.