How to Choose a Pet Carrier for Travel: Airline Sizing, Ventilation and Comfort

A good travel carrier lets your pet stand, turn around and lie down comfortably, has ventilation on several sides, closes securely and is leak-resistant. If you are flying with a cat or small dog in the cabin, it must also fit under the seat in front of you, within your specific airline’s size and weight limits, which differ between airlines and sometimes between aircraft. Get your pet used to the carrier weeks before the trip.

The rules below are general. Always confirm the current policy on your airline’s website before you book, since pet rules and fees change.

Hard-sided or soft-sided?

Many airlines accept either type in the cabin as long as it fits their maximum dimensions and is ventilated and leak-proof. Some list a lower maximum height for hard-sided carriers because soft ones can compress.

Getting the size right

1. Measure your pet standing: nose to the base of the tail for length, and floor to the top of the head (or ears, if upright) for height.
2. Compare with the carrier’s interior dimensions. Your pet should be able to stand without crouching, turn around, and lie down in a natural position.
3. Check the airline’s limits for carrier dimensions and, if they have one, the combined weight of pet and carrier. As of October 2026, several large US airlines cap in-cabin pets at around 20 pounds including the carrier, but this varies.
4. Do not squeeze a pet into a carrier that is too small to meet an airline rule. If your pet does not fit comfortably, ask about other options or reconsider flying with them.

Features to look for

• Ventilation on at least two or three sides, without gaps large enough for a paw or head.
• Secure zippers or latches. For curious cats, zipper clips or locking pulls help prevent escapes.
• A leak-resistant, washable base, plus an absorbent pad you can replace during the journey.
• A top opening or removable top, which makes it easier to lift a nervous cat out at the vet.
• A seatbelt loop so you can secure it in the car.
• Comfortable carrying for you: padded handles or a shoulder strap.
• ID on the carrier with your name and phone number.

Remember that ordinary carriers are not crash-tested. The nonprofit Center for Pet Safety tests and certifies some carriers for car travel if that matters to you. At minimum, belt the carrier in or place it on the floor behind a front seat so it cannot fly forward.

Flying with a pet: the basics

• Book early. Airlines usually limit how many pets are allowed in the cabin per flight, and fees apply. Many do not allow pets on certain routes.
• Check breed rules. Some airlines restrict short-nosed (brachycephalic) dogs and cats, particularly in cargo, because of breathing risks.
• Know the documents. Domestic US flights may or may not require a health certificate; international travel almost always involves specific requirements set by the destination country. The USDA APHIS pet travel site explains rules for leaving and entering the US; for the UK, see GOV.UK on taking a pet abroad. Our guide on taking a pet to another country covers the general steps.
• Emotional support animals are no longer treated as service animals on US airlines; most now travel under normal pet rules and fees.
• Ask your vet before flying with a pet that is elderly, pregnant, very young, has heart or breathing problems, or gets very anxious. Do not give any sedatives or calming medication unless your vet has prescribed them for this purpose; some can affect breathing and balance at altitude.

For road trips and US travel more broadly, see traveling with a dog in the US.

Getting your pet used to the carrier

Many pets only see their carrier on the way to the vet, so they learn to dread it. Start at least a few weeks before a trip:

1. Leave the carrier open in a room your pet likes, with a familiar blanket inside.
2. Toss treats or a favorite toy inside, or feed meals near and then inside it.
3. Once your pet walks in calmly, close the door for a few seconds, reward, and open it again.
4. Build up to a few minutes, then pick up the carrier and walk around the house.
5. Take short car rides that end somewhere pleasant or simply back home, not always at the vet.

Keep it calm and reward-based. If your pet panics, go back a step. Pets who stay very distressed even with gradual practice may need a vet’s advice before travel.

On travel day

• Follow your vet’s advice on feeding before the trip; a lighter meal a few hours beforehand is common to reduce nausea.
• Line the carrier with an absorbent pad and pack spares, wipes and a small bag.
• Carry your pet’s records and a recent photo.
• At airport security in the US, you will usually need to take your pet out and carry them through while the empty carrier is screened. A harness with a leash helps prevent escapes.
• Never leave a pet in a parked car, even briefly, in warm weather.

Bottom line

Choose a well-ventilated, secure carrier your pet can stand and turn in, check your airline’s exact dimensions and weight limits, and confirm documents early. The most important step is time: practice with the carrier for weeks so travel day is less stressful for everyone.

FAQ

What size carrier fits under an airline seat?

There is no single standard. Each airline publishes its own maximum dimensions, and under-seat space differs by aircraft. Check the airline’s pet policy and, if possible, the specific aircraft.

Can a cat and a dog share one carrier?

Most airlines allow only one pet per carrier, with limited exceptions. Check the airline’s rules.

Should I put food and water in the carrier?

For short trips, usually not. For longer journeys, a small spill-proof dish or offering water during breaks is common. Ask your vet for advice for your pet.

Is cargo travel safe for pets?

It carries more risk than cabin travel, especially for short-nosed breeds and in hot or cold weather. Many airlines restrict or no longer offer it. Discuss the options with your vet and the airline.