Airline Pet Carrier Size Guide: What Actually Fits Under the Seat

Every airline has a maximum carrier bag size listed on their website. And almost none of them are realistic for dogs bigger than a Chihuahua.

That’s the uncomfortable truth I had to learn the hard way. The numbers say one thing. Reality says another. And if you’re staring at your airline’s pet policy right now, trying to figure out how your perfectly normal-sized dog is supposed to fit into a bag that’s 23 cm tall — I’ve been exactly where you are.

Here’s what the size guides actually mean, what gets enforced, and how to make it work. Based on over 20 flights with a dog who technically doesn’t fit the “recommended” dimensions on most airline websites.

The Standard Dimensions (And Why They’re Misleading)

Most airlines list maximum carrier dimensions somewhere in the range of 55 × 40 × 23 cm (that’s roughly 22 × 16 × 9 inches). Length, width, height. Some airlines are a bit more generous, some a bit less, but those numbers are pretty typical.

The length and width are usually fine. Most soft-sided carriers fall within those ranges. The problem is the height. 23 cm. That’s barely 9 inches.

Sami is a West Highland White Terrier. He’s about 29 cm (11.5 inches) from paw to shoulder. When he lifts his head, it’s closer to 40 cm. In a 23 cm bag, he can lie down and he can turn around, but he cannot stand. Not even close.

And here’s the thing — Sami isn’t a big dog. He weighs about 7.7 kg. He’s on the smaller side of “small dogs.” If the stated dimensions don’t work for a Westie, they don’t work for most small-to-medium breeds. Jack Russells, Miniature Schnauzers, Cavalier King Charles Spaniels, Shih Tzus — all of them are going to have the same height problem.

What Actually Gets Checked

Here’s the part that changed everything for us: nobody actually measures the bag.

In over 20 flights, across multiple airlines in Europe and the US, not a single person has ever taken out a tape measure and checked our carrier dimensions. Not once. What they check is whether the bag fits under the seat in front of you. That’s the real test.

The seat clearance on most commercial aircraft is around 25-30 cm high, depending on the airline and aircraft type. So a bag that’s 28 or even 30 cm tall will still fit under most seats — especially a soft-sided bag that compresses slightly.

This is why we use a carrier that’s about 28-30 cm tall, even though the airline lists 23 cm as the max. It fits under the seat. The dog looks comfortable. Nobody has ever questioned it. The right carrier bag makes all the difference here — soft-sided bags compress and flex in ways that hard-shell carriers can’t.

The “Comfortable Fit” Rule

Beyond the raw dimensions, some airlines have an additional requirement: your dog must be able to stand and turn around inside the carrier with it closed. This is the rule that almost got us rejected at check-in once.

In practice, “stand” is interpreted loosely by most agents. If your dog can sit upright and turn around — even if they can’t stand at full height — you’re usually fine. The agents are looking for a dog that appears comfortable, not one that has ballroom-dancing space in there.

But the interpretation depends entirely on who you get at the counter. A strict agent might insist on seeing the dog stand. A relaxed one won’t even look. This is why I always say: prepare for the strict agent. If you can get through their check, you can get through anyone’s.

How to Pick the Right Size

Here’s the approach I’d recommend, based on what’s worked for us.

Measure your dog first. You need three measurements: length (nose to base of tail), height (paw to top of shoulder), and width (widest point, usually the chest). Write these down. These are your baseline.

Check your airline’s stated dimensions. Go to the airline website, find their pet policy (usually under “traveling with pets” or “carry-on pets”), and note the maximum carrier size. Remember, this is the bag size, not the dog size.

Choose a bag slightly larger than your dog needs, even if it exceeds the airline’s height by a few cm. I know this sounds risky. But a bag where your dog is comfortable is infinitely better than a bag that technically meets dimensions but makes your dog look cramped. A cramped-looking dog triggers agent concern. A comfortable-looking dog gets waved through.

Always go soft-sided. A soft carrier that’s 30 cm tall will compress to 26-27 cm when it’s pushed under the seat. A hard-shell carrier that’s 30 cm tall stays 30 cm tall. The flexibility of soft carriers gives you a built-in margin of error. Plus, soft bags are lighter, which matters when the weight limit includes the carrier.

Size by Dog Weight Range

Here’s a rough guide based on our experience and what I’ve seen from other flying-with-dog communities.

Under 4 kg (about 9 lbs): Standard small carrier. Most airline dimensions will work perfectly. Your biggest challenge isn’t size — it’s keeping the bag from looking too empty. A dog swimming in an oversized carrier looks weird too.

4-6 kg (about 9-13 lbs): Medium carrier. You should be fine with most airline dimensions, but start paying attention to height. Breeds with longer legs (like small terriers) may need slightly taller bags.

6-8 kg (about 13-17.5 lbs): This is where it gets tight. You’re at the upper end of what most airlines allow by weight, and your dog is probably too tall for the “recommended” carrier height. This is Sami’s range. Go for the largest soft-sided carrier you can find, prioritize height, and accept that the bag will likely exceed stated dimensions by a few cm. For terrier breeds in this weight range, I recommend at least 28 cm height.

8-10 kg (about 17.5-22 lbs): You need an airline with a higher weight limit — some European airlines allow up to 10-12 kg. Carrier size becomes even more critical. Check whether the airline even allows dogs this size in the cabin before you book.

Don’t Choose a Bag with Wheels

Quick but important note. I’ve seen wheeled pet carriers marketed for air travel, and they seem convenient — roll your dog through the airport instead of carrying them. Don’t do it.

Two reasons. The wheels add weight, which eats into your weight limit. And the wheel housing takes away from the bag’s internal height. So you get a heavier bag with less vertical space for your dog. It’s a bad trade.

Carry the bag. Get one with a comfortable shoulder strap and good handles. Your shoulders will thank you later, and your dog will have more room.

Got a specific airline you’re trying to figure out carrier sizes for? Drop it in the comments. Between our experience and the community here, we’ve probably got practical advice for your exact situation.