What You Cannot Pack in a Carry-On
The prohibited list, the items that catch people out, and the reverse rule almost nobody knows — the things that must go in the cabin and never in the hold.
We have not tested this gear. Every figure here is compiled from published manufacturer specifications and published airline policies, and the arithmetic is public so you can check it. This page contains affiliate links — see the affiliate disclosure.
The main categories TSA prohibits in a carry-on are liquids over 3.4 oz outside the one-quart bag, most sharp objects, firearms and ammunition, flammable and pressurized items, self-defense sprays, and tools longer than 7 in. Several of these are allowed in checked baggage instead — and a few common items are the reverse, banned from the hold and permitted only in the cabin.
- Liquids, gels, aerosols and pastes over 3.4 oz / 100 ml per container
- Knives of any blade length, box cutters, razor blades that are not in a cartridge
- Scissors with blades longer than 4 in from the pivot
- Firearms, ammunition, replica firearms and gun parts
- Self-defense sprays, including pepper spray and mace
- Flammable liquids, aerosol paint, lighter fluid, camping fuel
- Tools longer than 7 in, and any drill, crowbar or hammer
- Sporting goods that could be used as a bludgeon — bats, clubs, cues
This page summarizes published TSA rules. TSA officers have the final decision on any individual item at the checkpoint, and the authoritative list is TSA’s own What Can I Bring? database. Check it for anything unusual.
The liquids rule, stated precisely
The rule people call “3-1-1” is three separate constraints and most of the confusion comes from remembering only the first.
- 3.4 oz — the maximum size of any single container. Note that this is the container size, not the amount of liquid in it. A half-empty 8 oz bottle is prohibited.
- 1 quart — all those containers must fit in one clear, resealable quart-sized bag. A quart is 0.95 L, which is smaller than most people picture.
- 1 bag per passenger — you get one, and it comes out of the carry-on for screening.
“Liquid” is broader than it sounds: it includes gels, aerosols, creams, pastes and anything spreadable. Peanut butter, yoghurt, mascara, toothpaste and hummus are all liquids for this purpose. Solid deodorant, a bar of soap and a solid shampoo bar are not, which is why they are the standard workaround.
Exemptions exist for medically necessary liquids, breast milk, formula and baby food in reasonable quantities. Declare them at the checkpoint rather than hiding them in the quart bag — they are screened separately and they do not count against it. A toiletry bag with a separate clear pouch makes this materially faster.
The items that actually catch people
The prohibited list is mostly obvious. What costs people time and possessions is a much shorter list of items they assumed were fine.
| Item | Carry-on | Checked | The catch |
|---|---|---|---|
| Disposable and safety razors | Yes | Yes | The razor is fine. Loose blades and straight razors are not — the blade must stay in its cartridge. |
| Scissors | Under 4 in blade | Yes | Measured from the pivot, not overall length. Most nail scissors pass; most kitchen scissors do not. |
| Lighters | One, on your person | No | A common lighter is permitted in the cabin but prohibited in checked baggage. Torch lighters are banned outright. |
| Power banks and spare lithium batteries | Yes | No | Must travel in the cabin. This is a fire-safety rule, and it is enforced. |
| Snacks and solid food | Yes | Yes | Solid food is fine. Anything spreadable or pourable is a liquid and needs the quart bag. |
| Corkscrew with a foil cutter | No | Yes | The small blade makes it a sharp object. Bladeless waiter's friends are usually allowed. |
| Aerosol dry shampoo | Under 3.4 oz | Yes, limited | Aerosols are liquids for the quart bag, and checked aerosols are limited by volume too. |
| Knitting needles | Yes | Yes | Permitted, which surprises people. Circular thread cutters are not. |
The reverse rule: what must NOT be checked
This is the part of the rules that catches experienced travelers, because it runs the opposite way to everything else. A short list of items is prohibited in the hold and permitted only in the cabin, almost always for fire-safety reasons:
- Spare lithium batteries and power banks. Any loose lithium cell, including camera batteries and phone chargers with a battery in them, must be in the cabin where a fire can be seen and dealt with.
- E-cigarettes and vapes. Cabin only, and they must not be charged in flight.
- Lighters and matches. One common lighter or one book of safety matches on your person; neither in the hold.
- Anything with a large battery you cannot remove — some smart-luggage cases with non-removable batteries are prohibited as checked baggage entirely.
This matters more than it used to, because gate-checking a carry-on is now routine on full flights. If your bag can be taken from you at the door, the battery bank should not be inside it — keep it in your personal item, which stays with you.
A note on smart luggage
Suitcases with integrated batteries are permitted as carry-on where the battery can be removed, and are widely prohibited as checked baggage where it cannot. If you own one, know how the battery comes out before you are at a gate being asked to demonstrate it.
Outside the US
The 100 ml liquid limit is near-universal, but the details are not. Several major airports have installed CT scanners that permit liquids to stay in the bag and in some cases lift the volume limit entirely — and several have rolled that back again. The safe assumption when flying internationally is the strictest version of the rule: 100 ml containers in a one-liter bag, out of the case at the checkpoint.
Item-level rules differ too. Several countries prohibit items TSA permits, and a few permit items TSA does not. Check the departure airport’s own published rules for the outbound leg and the destination’s for the return — they are different authorities and they are not obliged to agree.