Liquids are the biggest difference. In a carry-on bag, the TSA limits liquids, aerosols, gels, creams and pastes to 3.4 ounces (100 ml) or less per item, all in one quart-sized bag; larger containers go in your checked bag. Some items go the other way: the TSA says devices with lithium batteries should travel in your carry-on.
Packing for a US flight means making the same call over and over: does this go in the bag I keep with me or the one I hand over at the desk? The Transportation Security Administration answers that item by item on its What Can I Bring list and its liquids rule page. This guide covers those security rules only. Bag sizes, weights and charges are set by each airline, so check yours separately.
Carry-on bag and checked bag side by side
| Item | Carry-on bag | Checked bag |
|---|---|---|
| Liquids, gels and aerosols over 3.4 oz (100 ml) | Not allowed, apart from the exemptions | Allowed: the TSA says pack them here |
| Mini bottles of alcohol | Allowed if they fit in your quart-sized bag | Allowed |
| Alcohol over 24% and up to 70% | Only in 3.4 oz (100 ml) containers | Up to 5 liters (1.3 gallons) per passenger, unopened retail packaging |
| Alcohol over 70% (over 140 proof) | Not allowed | Banned here too |
| Devices with lithium batteries | Allowed, and where the TSA says they should go | Special instructions apply |
| Aerosol insecticide | Not allowed | Yes, if not labelled as hazardous material |
| Axes and hatchets | Not allowed | Yes |
| Ammunition | Not allowed | Ask your airline; special packing rules apply |
| Baby carrier or antlers | Allowed if it fits the overhead bin or under the seat | Allowed |
The liquids rule in plain terms
The TSA's rule is short. You can bring a quart-sized bag of liquids, aerosols, gels, creams and pastes in your carry-on and through the checkpoint, as long as each container is 3.4 ounces (100 milliliters) or less. Taking that small bag out and putting it in the tray on its own helps screening go faster, and anything in it that alarms will need extra screening. You'll often hear it called the 3-1-1 rule.
There are exemptions for medications and for infant and child nourishment. Duty free liquids over 3.4 ounces can come through in your carry-on if you bought them abroad and you're flying into the United States with a connecting flight, provided they're in a transparent, secure, tamper-evident bag from the retailer, you have the original receipt and you bought them within 48 hours. Even then, the TSA recommends putting them in your checked bag, and any liquid over the limit that isn't in a sealed bag must go in checked baggage.
Why lithium batteries stay in the cabin
This one runs against the usual logic of putting anything awkward in the hold. The Transportation Security Administration says devices containing lithium metal or lithium ion batteries should be carried in carry-on baggage, while most other consumer devices with batteries are allowed in either bag. It points travellers to the FAA's regulations for portable electronic devices.
Expect your electronics to get attention at the checkpoint. The TSA asks you to take anything larger than a phone, such as a laptop, tablet, e-reader or handheld game console, out of your carry-on and into a bin with nothing on or under it. Officers may also ask you to power a device up, and the TSA says powerless devices won't be allowed onboard. Hair dryers, electric shavers and electric toothbrushes don't need to come out.
Alcohol: where the checked bag allows more
Alcohol is the clearest case of the hold being more generous. The TSA says drinks with 24% alcohol or less aren't subject to limits in checked bags. Between 24% and 70%, you're limited to 5 liters (1.3 gallons) per passenger, in unopened retail packaging. Anything over 70%, including grain alcohol and 151 proof rum, isn't allowed in either bag.
In a carry-on, mini bottles must fit comfortably in your single quart-sized bag. The TSA also reminds travellers that FAA rules don't let you drink your own alcohol on board unless a flight attendant serves it, and suggests checking with your airline before bringing any.
What happens to each bag at security
The TSA says it screens about 3.3 million carry-on bags and about 1.3 million checked bags for explosives and other dangerous items every day. Most checked baggage is screened without a physical search, but if an officer does open yours, the TSA leaves a notice of baggage inspection inside. It holds master keys for Safe Skies and Travel Sentry locks, so those may not need cutting. Lost or damaged during screening? You can file a claim with the TSA; if it happened on the way to the plane or the baggage claim, that's one for your airline.
Food is usually fine in a carry-on: the TSA says fruit, health bars and sandwiches can generally stay in the bag. Flying into the US, the TSA encourages putting powders over 12 oz (350 mL) in checked bags. And whatever the list says, it's clear that the final decision on whether an item goes through the checkpoint rests with the TSA officer. For the rest of your packing, my business trip packing list and guide to the travel backpacks worth a look pick up where this leaves off.
My advice on packing a carry-on or checking a bag
It depends on what's in the bag rather than its size. If you're carrying full-size toiletries, bottles of wine or spirits, tools or anything with a blade, a checked bag is where the Transportation Security Administration wants them. If you're travelling with laptops, power banks or anything else that runs on lithium batteries, keep them in your carry-on. Check anything unusual against the TSA's What Can I Bring list before you pack, and ask AskTSA if it isn't there.
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Frequently asked questions
Can I take liquids over 3.4 ounces in a carry-on bag?
Not usually. The TSA limits carry-on liquids to 3.4 ounces (100 ml) per container in one quart-sized bag. Medications and infant nourishment are exempt, and duty free liquids bought abroad in a sealed tamper-evident bag can travel on connecting flights into the US.
Can I put a power bank in my checked bag?
The TSA says devices containing lithium metal or lithium ion batteries should be carried in carry-on baggage, so keep them with you.
How much alcohol can I pack in a checked bag?
Drinks of 24% alcohol or less aren't limited. Between 24% and 70%, the TSA allows up to 5 liters (1.3 gallons) per passenger in unopened retail packaging. Over 70% isn't allowed.
Who decides if an item can go through security?
The TSA officer. Its What Can I Bring page says the final decision on whether an item is allowed through the checkpoint rests with the officer, even for items generally permitted.
Will the TSA open my checked bag?
It might. The TSA says most checked bags are screened without a physical search, and if your bag is inspected you'll find a notice of baggage inspection inside.
What if my item isn't on the TSA list?
Ask the AskTSA team. The TSA says it answers questions 365 days a year, with live help from 8 am to 6 pm Eastern Time.
