How to measure your pet for an airline carrier
Two measurements decide everything: length from nose to the base of the tail, and height from the floor to the top of the head (ears up) while standing. Airlines then apply one rule — your pet must be able to stand up and turn around inside the carrier — and the carrier itself must fit under the seat.
Have a dog? Check your breed's standard weight against each airline's cabin cap →
The two measurements, done right
Measure while your pet stands naturally. Length runs nose to tail base (the tail itself doesn't count — it folds). Height runs floor to the top of the head or ear tips, whichever is higher. Add a couple of inches of comfort to each and you have the smallest carrier that's fair to your pet.
The stand-and-turn rule
Every major airline phrases its in-cabin requirement roughly the same way: the pet must be able to stand and turn around comfortably in the carrier. Gate agents check the pet, not a tape measure — a visibly cramped animal is what gets refused. That rule sets your carrier's minimum; the under-seat limit sets its maximum.
Where the squeeze happens
Height is the tight dimension: seats sit roughly 8–11 inches off the floor depending on airline and aircraft, which is why soft-sided carriers with a little flex dominate our fit rankings, and why the published number is optimistic. Taller cats and long-backed breeds hit this ceiling first.
Putting it together
Once you have length and height: pick your airline on the fit matcher to see which carriers clear its published limit, or start from a carrier you like — each carrier page shows exactly which airlines it fits. The right buy is the largest carrier that fits your airline and still gives your pet the stand-and-turn room.
Next: the fit matcher · best carriers ranked by fit · the under-seat truth
Which carrier fits your airline?
Every airline sets its own under-seat size, so the right carrier depends on who you fly. Pick yours for the carriers that clear its published limit: Southwest Airlines · American Airlines · Delta Air Lines · United Airlines · Alaska Airlines · JetBlue · Frontier Airlines · Air Canada · WestJet · all airlines →
Flying over Thanksgiving or Christmas? Read the holiday pet-travel guide →
Carriers that clear the most airlines
Ranked by how many of the 58 airlines with a published cabin limit each one clears at its published size — the same computation behind every fit verdict on this site.
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Sherpa Original Deluxe (Small)Mr. Peanut's Gold Series Mini (Low-Profile)Petmate Soft-Sided Kennel Cab (Medium)Mr. Peanut's Gold Series Standard (Expandable)Common questions
Should the carrier be bigger or smaller than my pet?
A little bigger — a few inches longer than your pet's nose-to-tail-base length, and tall enough to sit and lie naturally. Then it must still fit under YOUR airline's seat: that's the squeeze this whole site exists to resolve.
My pet is right between carrier sizes — which way do I go?
For flying, down. Airlines enforce the carrier's fit under the seat, and a slightly snug soft-sided carrier that your pet can still stand and turn in beats a roomy one that gets refused at the gate.
Does my pet's weight matter, or just size?
Often, yes — 36 of 62 cabin-allowing airlines we track (58%) publish a COMBINED pet-plus-carrier weight cap, not just a size limit. Check your airline's hub page here; each lists the official figure with its source.