Airline Pet Carrier Size Chart: What Fits Under Each Seat in 2026

Travel · PetzDay Editorial · 2026-11-13

The exact in-cabin pet carrier limits for Delta, American, United, Southwest and Alaska, which soft-sided bag covers all five, and how to measure a carrier so the gate agent does not send you back.

You cannot buy a pet carrier by looking at it. The number that decides whether your dog flies is the interior height of your carrier against the under-seat clearance of your specific aircraft, and the five largest U.S. airlines publish five different limits — from 7.5 inches on a hard-sided kennel at United to 11 inches on a soft-sided bag at Delta and American.

This page is the measurement sheet: every published limit, what actually fits under the seat, and the one bag shape that clears all five airlines.

This post contains affiliate links. If you buy through them, PetzDay may earn a commission at no extra cost to you. Carrier limits below are the airlines' published figures and should be confirmed for your aircraft before you buy.

A soft-sided carrier is the type most U.S. airlines require in the cabin. Photo: Veterinarian Pet Alliance / Wikimedia Commons (CC BY 4.0).

The size chart

Fees are one way, per carrier. Carrier numbers are each airline's published maximum, exterior dimensions. "Soft" means soft-sided bag, "hard" means rigid kennel.

Note what the table does not show: the differences are in height, not width. All five allow roughly 17–18 inches of length. The spread is 9.5 to 11 inches of height on a soft bag — enough that a bag sold as "airline approved" can fail on one airline and pass on another.

One carrier that fits all five airlines

Only one size clears every carrier limit above: a soft-sided bag no larger than 17 × 11 × 9.5 inches. That is Alaska's limit, and it is 0.5 inches under Southwest's 10 inches and 1.5 inches under the 11 inches Delta, American and United allow.

That is the safe buy. In practice:

• 17 × 11 × 9.5 in — clears all five. Slightly small, but never rejected.
• 18 × 11 × 11 in — clears Delta, American and United. Fails Alaska and Southwest on paper.
• 18 × 10.5 × 10 in — clears Southwest. Fails Alaska's 17-inch length if measured tight.

If you fly one airline and know which, buy to that airline's number. If you fly whoever is cheapest, buy 17 × 11 × 9.5 and stop reading.

A soft-sided carrier: mesh on three sides, compressible, no rigid frame to fight the seat. Photo: Sciencia58 / Wikimedia Commons (CC0).

Top-Side Expandable Pet Carrier, Treat Window,18x11x11 Airline Approved

18 × 11 × 11 in clears Delta, American and United — check Alaska and Southwest first

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How to measure a carrier the way the gate measures it

• Measure the outside, including wheels, pockets and the frame. Airline limits are exterior dimensions, and a stuffed side pocket is part of the bag.
• Measure height to the highest rigid point. A soft bag squashes; a bag with a wire rim does not.
• Measure your dog inside the bag, not on the floor. The dog must stand, turn around and lie down without touching the sides — a dog who fits the bag but cannot turn around does not fit the rule.
• Check the under-seat space on your route, not the airline's fleet. Seat pitch varies by aircraft, and bulkhead rows have no seat ahead to stow under at all.

Under-seat space varies by aircraft and seat row — a bulkhead or exit row has no seat ahead to stow a carrier under. Photo: Douglas P. Perkins / Wikimedia Commons (CC BY-SA 3.0).

Hard-sided kennels: the stricter rules

Hard kennels are the classic "travel crate" shape, and they are where people get caught.

• United allows 17.5 × 12 × 7.5 inches — 7.5 inches of height is the tightest limit at any of the five.
• American allows 19 × 13 × 9 inches on mainline aircraft, and 16 × 12 × 8 inches on American Eagle regional jets.
• Delta does not publish a single hard-sided number; it tells you to check under-seat space for your aircraft.
• Southwest publishes no hard-sided limit.
• Alaska does not accept hard kennels in the cabin at all — soft-sided only.

A rigid kennel has to meet stricter dimensions, and Alaska refuses them in the cabin outright. Photo: Chachacha369 / Wikimedia Commons (CC BY-SA 3.0).

What "airline approved" actually means

It means nothing official. There is no certification body, no registry, and no airline that licenses carriers for the phrase. It is a marketing claim that usually means "we sized this near a common limit" — and the limit it was sized to may not be your airline's.

What the airlines actually check at the gate:

• the carrier fits under the seat in front of you
• the dog is inside it and cannot get out
• the bag is leak-proof and ventilated on at least three sides
• the zips hold

Buy on measurements, not labels. If a listing has no exterior dimensions, skip it.

The two carrier mistakes that get dogs denied

A backpack or a sling. They are not pet carriers for airline purposes, however well they carry a small dog. No under-seat fit, no leak-proof base, and the dog's head is out.

A carrier that only fits empty. Load the dog before you fly, put the bag on the floor, and see if it still slides under a chair back. A bag that sags once the dog is in it is not the size on the label.

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After the carrier: the airport steps that surprise people

A pet relief area after security is the one stop worth planning before the gate. Photo: The Eloquent Peasant / Wikimedia Commons (CC0).

• A pet reservation is not part of your ticket. Reserve by phone or chat and get it in writing — Southwest sells pet space by phone only.
• Security means the dog comes out. The carrier goes through the X-ray; the dog walks through with you on a leash.
• Pet relief areas sit after security at most large U.S. airports. Find it before you board, not after.
• The fee is per direction. A round trip is two fees, and a connection on a separate ticket can be a third.

For fees, cabin rules and what happens when the dog is too big, the airline pet fee comparison covers all five carriers in one place. If the trip is by car instead, the road trip checklist starts with restraint, because a carrier is not a crash box.

FAQ

What size pet carrier is allowed on airplanes?

For the five largest U.S. airlines, a soft-sided carrier up to 17 × 11 × 9.5 inches clears every one of them. Delta, American and United accept 18 × 11 × 11 inches, Southwest caps soft bags at 18 × 10.5 × 10, and Alaska is the strictest at 17 × 11 × 9.5 with no hard kennels at all.

Is an 18 × 11 × 11 carrier airline approved?

It is accepted by Delta, American and United. It is not within Alaska's cabin limit (17 × 11 × 9.5) and it exceeds Southwest's height cap of 10 inches. "Airline approved" on a listing is not a certification — check the number against the airline you are actually flying.

What size carrier does Southwest allow?

Southwest publishes a soft-sided maximum of 18 × 10.5 × 10 inches and does not publish a hard-sided limit. The carrier still has to fit under the seat in front of you, and Southwest sells pet space by phone only, so reserve before you buy a bag.

Can I use a hard-sided kennel in the cabin?

On American and United, yes, within their published limits — 19 × 13 × 9 inches on American mainline (16 × 12 × 8 on Eagle) and 17.5 × 12 × 7.5 on United. Not on Alaska, which accepts soft-sided carriers only in the cabin.

How do I know if my dog fits the carrier?

The dog must be able to stand, turn around and lie down inside the closed carrier without touching the sides. Most dogs that pass are under about 15–20 pounds, and some smaller dogs still fail the turn-around test. Measure the dog inside the bag before you fly.

Do I need a different carrier for each airline?

Only if you are flying Alaska or Southwest with an 18 × 11 × 11 bag. One 17 × 11 × 9.5 inch soft-sided carrier covers all five airlines, which is why it is the size worth buying if you do not want to track five limits.

References

• Delta Air Lines — Pet travel overview
• American Airlines — Traveling with pets
• United Airlines — Traveling with pets
• Southwest Airlines — Pet policy
• Alaska Airlines — Pets in cabin
• U.S. DOT — Flying with a pet
• USDA APHIS — Take a pet from one U.S. state to another

All web sources accessed November 13, 2026. Airline carrier limits change with aircraft and policy; confirm the dimensions for your flight before buying.

Last reviewed: November 13, 2026.