No carrier is approved by an airline: each one publishes the space under the seat your bag has to fit, and Delta's is 11 inches tall where JetBlue's is 8.5. The Sherpa Original Deluxe in Medium copes with that spread better than any bag here, for about $63. It's 17 by 11 by 10.5 inches, fits Delta and United as it comes, and a spring frame at the back presses down for the lower seats on Alaska and JetBlue; if an airline still turns it away for its size, Sherpa refunds your fare.
Southwest is the catch: its limit is half an inch narrower and half an inch lower than the bag, and the frame only helps with height. For that airline and a cat under 9 pounds, the Petsfit Small fits as it comes.
Your cat weighs up to 16 pounds and you fly Delta or United, or don't mind pressing the bag down for a lower seat.
Skip it if
Your cat weighs more than 16 pounds, the limit Sherpa puts on the Medium.
Sherpa sizes this bag for a pet up to 9.5 inches tall and 16 inches long. That isn't the nose-to-tail length you'd measure for a litter box: a cat rides lying down, usually curled, so the real test is your cat inside it at home with the zipper closed. It opens on the top and the side, so a cat who won't walk in can be lowered in from above, and at the vet you can lift her out the same way.
The back of the frame is spring wire that pushes down several inches to fit under airplane seats. You'll need about an inch of that for Alaska, two for JetBlue, and half an inch on a United 737 MAX. The Medium is part of Sherpa's Guaranteed On Board program: you fill out a form before the flight, and if the airline refuses the bag for its size, Sherpa refunds your ticket and the pet fee, on major airlines and on domestic flights in the US and Canada.
Before you fly with it
The length fits every airline here; the height is what you press down. Try it at home under a chair, with your cat inside, before the day of the flight.
Where it falls short
The Large is 19 inches long, too long for every airline here: buy the Medium.
A 16-pound cat fits by the label but has little room to turn.
Half an inch wider than Southwest's limit; the soft sides give, but the frame doesn't help there.
2Best for plane and car
2. Sleepypod Air
Roomy at 22 inches, it folds down to 16 by 8 inches for the seat, and it doubles as a car seat.
The flight is one leg of a longer trip, with a car ride at either end.
Skip it if
You fly once a year to see family. About $200 buys three of the Sherpa.
Where it falls short
Folded down, the inside gets small; it's a bag to fold at boarding and open again on the ground.
Read more about the Sleepypod AirShow less
At about $200, this is the priciest bag here. It's 22 inches long at full size, longer than any airline allows, so your cat gets the full length in the car and at the gate. Then the ends fold in, and Sleepypod lists it at 16 by 10.5 by 8 inches, the only bag here that goes inside all five airlines' limits, JetBlue's 8.5 inches included.
Sleepypod makes it as a bed and a car seat as well as a carrier, so the same bag can be strapped in for the drive to the airport. The top and both ends open, and the bedding inside goes in the washing machine. It's rated for cats up to 17.5 pounds, a little more than the Sherpa.
3Best for small cats
3. Petsfit Small Expandable Cat Carrier
At 16 by 10 by 9 inches it sits inside Alaska's and Southwest's limits as it comes, for a cat under 9 pounds.
Your cat is small, under 9 pounds, and you fly Southwest or Alaska.
Skip it if
Your cat weighs more than 9 pounds. Get the Sherpa instead.
Where it falls short
Nine pounds is a low limit; plenty of grown cats are heavier.
At 9 inches tall, it's still half an inch over JetBlue's 8.5.
Read more about the Petsfit SmallShow less
Nothing to press or fold at the gate: at 16 by 10 by 9 inches, the Petsfit Small is inside Alaska's limit of 17 by 11 by 9.5 and Southwest's of 18 by 10.5 by 10, with room to spare. The empty bag weighs about 2.1 pounds.
Once you're past security, one mesh side unzips and opens the bag to 17.3 by 16 inches, so a kitten can stretch out at the gate. Zip it back before you board. The bag folds flat in your suitcase for the trip home, too.
4Best expandable
4. Petsfit Medium Expandable Cat Carrier
Inside Delta's and United's limits when zipped, and a side panel that opens to 20 by 17 inches so your cat can stretch out before boarding.
You have a long layover, or a cat who calms down once she can lie flat.
Skip it if
You fly Southwest, JetBlue, Alaska or a United 737 MAX: at 11 inches tall, it's over their height limits as listed.
Where it falls short
Too tall for three of the five airlines here.
The 13-pound limit is lower than the Sherpa's.
Read more about the Petsfit MediumShow less
At 17 by 11 by 11 inches, the Petsfit Medium is inside Delta's and United's usual limits, and it's built for the hour before boarding. One side unzips and the bag grows to 20 by 17 inches, close to a small playpen, while you wait at the gate. It's rated for cats up to 13 pounds, and Petsfit asks you to go by your cat's measurements before her weight.
The base has a stiff board under the pad, so the bag doesn't sag in the middle when you carry it, and there's a strap that slides over the handle of a rolling suitcase.
5Best backpack
5. Sherpa Deluxe Convertible Carrier & Backpack, Medium
The Original Deluxe half an inch narrower, with the same fare guarantee and padded backpack straps for a long walk to the gate.
You'll walk a long way between gates, or carry a bag of your own as well.
Skip it if
Your cat hates being carried upright. The backpack hangs her on end.
Where it falls short
Upright on your back, your cat stands on one end, which some cats don't like.
Straps and buckles to tuck away before it goes under the seat.
Read more about the Sherpa backpackShow less
This is the Sherpa with straps, half an inch narrower at 10.5 inches, with the same 16-pound limit and the same fare guarantee as the Original Deluxe. That half inch puts it inside Southwest's width; there, only the height is half an inch over. The straps clip off, so under the seat it's an ordinary carrier on its side.
The extra $14 or so makes sense in a big airport, or on a trip with a toddler, a suitcase and a cat at the same time. There's a short tether inside that clips to your cat's harness, handy when you unzip the top to check on her.
6Best under $30
6. PetAmi Airline Approved Pet Carrier, Small
A plain soft bag with locking zippers and a fleece pad, for about $29, rated by PetAmi for cats up to 18 pounds.
You fly once, maybe twice, and want a bag that does the job for about $29.
Skip it if
You fly JetBlue or Alaska. At 11.2 inches tall, it's well over their limits.
Where it falls short
No frame to push down, so it squeezes rather than folds.
Too tall for JetBlue and Alaska.
Read more about the PetAmiShow less
For one trip a year, this does the job. It has locking zippers, an inside clip for your cat's harness, mesh on several sides and a fleece pad. It's rated for cats up to 18 pounds, the highest limit here, but an 18-pound cat in a bag 17 inches long lies curled tight; read that number as what the bag holds, not what a cat that size will enjoy.
The listed height is 11.2 inches, a fifth of an inch over Delta's and United's 11, so as sold it fits none of the five. The sides are soft and give that much under a seat, but you're relying on the squeeze, where the Sherpa is built for it.
Airline rules as of October 2026. Sizes are length by width by height, in inches; fees are per carrier, each way. Every airline here wants the whole bag under the seat in front of you, and your cat in it with the zipper closed, from the gate to the end of the flight. American's policy isn't in this table; check aa.com before you book.
Airline
Size (in)
Fee
Delta
18 × 11 × 11 recommended, soft-sided
$150
United
Soft 18 × 11 × 11, hard 17.5 × 12 × 9; 10 tall on a 737 MAX
$150
Southwest
18 × 10.5 × 10
$125
JetBlue
17 × 12.5 × 8.5
$150
Alaska
17 × 11 × 9.5, soft-sided only
$100
The cat has to fit in comfortably: Southwest says your pet must be able to stand up and move around inside, and JetBlue that it must be able to turn around with the bag closed. Delta, United, JetBlue and Alaska also cap the number of pets on each flight, so book your cat's spot when you book your own seat. None of the five sets a weight limit for the cat on these pages (United says outright there isn't one); size is what counts. Delta gives its size as a recommendation and adds that the space under the seat changes from one plane to the next, which is why a soft bag is the safer choice.
Each carrier against each airline
Each bag at its listed size. Only the Sherpa Original's frame is built to press down several inches; the others are soft bags that give a little, no more.
Carrier
Fits
Over by
Sherpa Original
Delta, United
½ in tall on a 737 MAX, 1 in on Alaska, 2 in on JetBlue; ½ in wide and tall on Southwest
Sleepypod Air
All five, folded
None, folded
Petsfit Small
Delta, United, Southwest, Alaska
½ in tall on JetBlue
Petsfit Medium
Delta, United
1 in tall on a 737 MAX, 1½ in on Alaska, 2½ in on JetBlue; ½ in wide and 1 in tall on Southwest
Sherpa backpack
Delta, United
½ in tall on a 737 MAX and Southwest, 1 in on Alaska, 2 in on JetBlue
PetAmi
None
0.2 in tall on Delta and United, 1.2 in on a 737 MAX and Southwest, 1.7 in on Alaska, 2.7 in on JetBlue
Which carrier for which airline
Delta or United: the Sherpa as it comes (press it down half an inch on a United 737 MAX).
Southwest: the Petsfit Small for a cat under 9 pounds; for a bigger cat, the Sleepypod Air folded.
Alaska: the Petsfit Small, or the Sherpa pressed down an inch.
JetBlue: the Sleepypod Air folded, the only bag here inside 8.5 inches as listed; the Sherpa needs pressing down two inches.
Before the flight
Your cat has to be at least 8 weeks old on Delta, Southwest and Alaska. On Southwest and Alaska the carrier counts as your personal item or your carry-on, so plan to pack one bag fewer. Alaska won't seat you in an exit row or a bulkhead row with a pet, and United suggests a health certificate from your vet even for a flight inside the US. In the weeks before, leave the carrier open on the floor at home with a towel she has slept on and a few treats inside, so it's a familiar place by the day you leave. Line the bottom with something absorbent. VCA says most cats fly without any medication; if you're thinking of a sedative, ask your vet first, since Alaska advises against them at altitude.
Soft-sided or hard-sided for flying?
Soft-sided. Delta and Southwest both recommend it, and Alaska doesn't let a hard-sided carrier into the cabin at all. A soft bag gives a little where the seat frame sits, and a plastic one doesn't give at all. Keep the hard-sided carrier for the car and the vet, where its top door and solid floor are a real help.
Best airline carrier for a large cat
None of these airlines weighs your cat; what stops a big cat is the box. The highest limits here are 16 to 18 pounds (16 for the Sherpa, 17.5 for the Sleepypod Air, 18 for the PetAmi). A 15-pound cat lying in a 17-inch bag is fine for a two-hour flight; an 18-pound Maine Coon is curled tight. If your cat is long rather than heavy, the Sleepypod Air is the roomiest choice, since she has the full 22 inches until boarding and again after landing.
Getting through airport security with a cat
The bag goes through the X-ray, and your cat doesn't. The TSA asks you to take your pet out just before screening, put the empty carrier on the belt, and carry your pet through the metal detector. That's the moment a cat gets away, and the TSA says cats are often skittish out of the carrier. Put a harness on her at home, clip the leash on before you unzip, and if she's likely to panic, ask an officer to screen her in a private room.
Can you use a backpack carrier on a plane?
Yes, as long as it meets your airline's size limit lying on its side under the seat. The Sherpa backpack does on Delta and United as it comes. A backpack built for walks can be deeper than it looks from the front, so check all three numbers against the table before you buy one for a flight.
Who this is for
These bags are for cabin travel inside the US, with a cat small enough to ride under the seat in front of you. If the carrier is mainly for the vet and the car, a hard-sided one with a top door is easier to load a reluctant cat into.
What to look for in an airline cat carrier
Your airline's box
Check the size on your airline's pet page, and on the plane you're flying if it lists one. The lowest limit on your trip is the one that counts.
Your cat lying down, not just her weight
Measure her curled up or lying on her side, and compare with the bag's length, not only the pound limit.
Locking zippers and a clip inside
A clip that attaches to her harness means an open zipper at the gate isn't an escape.
A top opening
You can check on her, or lower her in, without unzipping the whole side.
A well-made bag, but Mr. Peanut's says it's designed for pets lying down and yours may not be able to stand in it. Southwest requires that your pet can stand up and move around.
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Common questions
What is the best airline-approved pet carrier?+−
For a cat, the Sherpa Original Deluxe in Medium: it fits Delta and United as it comes, presses down for lower seats, and Sherpa refunds the fare if the airline turns the bag away for its size. For trips with a car ride at both ends, the Sleepypod Air.
What size cat carrier is airline approved?+−
It depends on the airline. Delta recommends 18 by 11 by 11 inches, Southwest allows 18 by 10.5 by 10, Alaska 17 by 11 by 9.5, and JetBlue 17 by 12.5 by 8.5. A soft bag around 17 by 10.5 by 10 inches that can be pressed lower fits most of them.
How do you know if a pet carrier is airline approved?+−
By its size, not its label: "airline approved" is the seller's claim. Compare the bag's dimensions with your airline's pet page, and check that your cat can turn around inside it with the zipper closed.
Is there a TSA-approved cat carrier?+−
No. The TSA screens you and your cat at the checkpoint; it doesn't approve carriers. The size that matters is your airline's, which is why the tables above go airline by airline.
Do cats prefer hard or soft carriers?+−
For flying, soft is the one that works, since airlines recommend it and Alaska requires it. For the vet, a hard carrier with a top door is easier, because you can lift your cat straight out.
What is the best cat carrier for a 20 pound cat?+−
None of the bags here is rated for 20 pounds: the PetAmi goes highest, at 18, and the Sleepypod Air to 17.5. A cat that size will be curled tight in any bag that fits under a seat, so ask your airline what it offers before you buy.
The verdict
Get the Sherpa, then fill out its form
Get the Sherpa Original Deluxe in Medium, and fill out its Guaranteed On Board form as soon as you've booked. The fare refund only works if the form went in before the flight, and it's the one thing no other bag here gives you if a gate agent says no.
