What Size Pet Carrier Can Go In-Flight?

Crying babies, confiscated shampoo, cramped leg room -- the pains of air travel. We may have to shell out for a first-class fare to get a bit of room to stretch, but our pets shouldn’t have to suffer with us if we fly coach. Transporting your pup in the biggest allowable carrier ensures he has room to relax. But finding an individual airline's maximum pet carrier size isn’t easy to find. Airlines have differing policies, so be sure to check with airlines before you book a flight with your pet.

Allowable pet carrier dimensions vary for each airline, and in some cases even the seat. Although it's rare, some airlines assign different carrier limits for particular seats, meaning you may have more or less space than the person next to you, due to restrictions on under-seat space. Some airlines don’t allow animals to travel in the passenger cabin at all. Among those that do, carrier size regulations differ by a few inches. Frontier Airlines boasts the largest carrier size permitted at 24 inches wide, 15.5 inches deep and 9.5 inches tall, but that size is only allowed on some of its aircraft, according to Frontier data. Alaska and United share the tightest size restrictions, with a maximum size of 17 inches wide, 12 inches deep and 7.5 inches high for hard-sided kennels. Both airlines allow for slightly larger kennels if the sides are soft.

Don’t purchase a carrier marked as TSA-approved or airline-approved and expect a guaranteed fit. Because there is no standard size limit, you must check with your particular airline to be sure the kennel you purchase fits its requirements -- in both size and construction -- even if the pet porter packaging claims it’s allowed. You’ll also need to know the added fee for traveling with your pet, as well as whether you need to make a reservation for him to fly with you. Whatever the carrier size limit, your pup has to be able to stand up and turn around. Airline employees reserve the right to turn away animals who seem cramped or uncomfortable in their cages. They ask that all critters large and small can turn around and stand comfortably in their cages.

In addition to size constraints, airlines place numerous other requirements on pet travel carriers. Even if your airline doesn’t require some of the steps, the airline's personnel should help guarantee smooth travels for your furry friend. Mark the outside of the kennel with your name and home address, and write LIVE ANIMAL in letters at least 1 inch high. Put arrows pointing toward the top end of the pet carrier. The ASPCA recommends you attach his photo to the top of the crate and carry another copy with you in case he escapes. Microchipping adds an extra layer of assurance to the worst-case scenario of a pet on the run.

When traveling with your pet, a proper pet carrier isn’t the only regulation you'll have to follow. The USDA requires you to offer your pets food and water within four hours of checking in at the airport. Carry a leash in case you must remove him from the carrier at the request of airport staff, but be aware you may take him out only if directed. You’ll need a health certificate from your veterinarian, too, usually dated within about 10 days of travel. Your pet counts as a carry-on, so don't think you can get away with both Sparky and a suitcase.