You're standing in line at the gate. Your heart does that weird little flutter when you see the Southwest agent eyeing the line. They aren't looking at faces; they’re looking at wheels. Specifically, they’re looking at the wheels of your carry on luggage Southwest style—the bags that look just a little too puffed out to fit in the overhead bin of a Boeing 737.
Honestly, Southwest is the outlier in the best way possible. While every other domestic carrier is nickel-and-diming you for the privilege of bringing a backpack, Southwest still lets you bring a carry-on and a personal item for free. Plus those two checked bags. But here’s the kicker: their bins aren't infinite. If you show up with a bag that’s technically a "medium" suitcase pretending to be a "small" one, you’re going to have a bad time.
The official rule is simple. Your bag must be $24 \times 16 \times 10$ inches.
Most people mess this up because they forget about the wheels. Or the handles. If those plastic bits stick out past 24 inches, you’re technically over the limit. Southwest pilots and flight attendants will tell you—usually off the record—that the 737-800 and the MAX 8 have much roomier bins than the older 700 series. If you end up on an older plane, those "legal" 24-inch bags sometimes have to go in sideways, which makes you the most hated person on the plane because you just took up space for three bags.
The dimensions that actually matter for carry on luggage Southwest
Don't trust the tag on the suitcase at the department store. It might say "Airline Approved," but that's a lie. Every airline has different "approval."
Southwest gives you a bit more breathing room than United or American. Most "legacy" carriers cap you at 22 inches. Southwest gives you 24. That extra two inches is basically the difference between packing an extra pair of boots or leaving them at home. But—and this is a big "but"—if you are connecting to a smaller regional jet on a different airline later in your trip, that Southwest-sized bag is going to get tagged and tossed into the cargo hold faster than you can say "boarding group A."
The personal item is the second half of the puzzle. It needs to be $16.25 \times 13.5 \times 8$ inches.
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Think of it as the "under the seat" bag. If you’re sitting in the bulkhead row (the very first row), you don’t have a seat in front of you. This means everything has to go up top for takeoff and landing. If the flight is full and you’re in Boarding Group C, you might find yourself separated from your gear.
I’ve seen it happen. A guy in C-42 tries to shove a massive leather duffel into a bin that’s already packed with thin hardshell rollers. It doesn't fit. The flight attendant sighs. The whole boarding process stops. Everyone stares. He has to walk back to the front of the plane to gate-check it. It sucks.
Hard shell vs. Soft side: The Great Debate
There is a real strategy here. Hard shell suitcases are great because they protect your stuff if the bag ends up being checked. They don't crush. However, they don't squish either.
If your carry on luggage Southwest is a soft-sided bag, you can often "persuade" it into a tight overhead bin. You can't do that with a polycarbonate shell. If that shell is a half-inch too wide, it’s game over.
Brands like Away or Monos are popular, but their "Plus" or "Large" carry-ons are pushing the limit. The standard Away carry-on is $21.7 \times 13.7 \times 9$, which is well within Southwest’s $24 \times 16 \times 10$. You’re actually leaving space on the table there. If you want to maximize every square inch, look at bags specifically designed for Southwest’s unique dimensions, like certain Travelpro models or the Osprey Farpoint 40.
What you can't actually bring (The stuff people forget)
We all know about the 3-1-1 liquids rule. TSA still cares about your shampoo. But Southwest passengers often get caught up in the "two free checked bags" mentality and forget that the carry-on rules are about safety, not just space.
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- Self-balancing scooters: Hoverboards are a no-go. Lithium batteries are the enemy.
- Sharp objects: Obvious, right? But people still try to bring knitting needles or tiny Swiss Army knives.
- The "Personal Item" loophole: A purse counts. A laptop bag counts. A camera bag counts. You get one. If you have a purse and a laptop bag and a roller, you have three bags. You’ll be asked to stuff your purse into the laptop bag before you step on the jet bridge.
If you're traveling with a pet, that pet carrier counts as either your carry-on or your personal item. You can't have a dog, a roller bag, and a backpack. The math just doesn't work for the gate agents.
The "Sizer" Box Reality
You’ll see those metal sizer boxes near the Southwest check-in counters. Most people walk right past them.
Use them.
If your bag slides in easily, you’re golden. If you have to jump on it to make it fit, you’re taking a risk. Southwest is generally "nicer" than Frontier or Spirit—they aren't incentivized to catch you with a commission for every bag they move to the hold—but they still have to close those bin doors. If the door won't latch, the bag goes downstairs.
Strategies for the Boarding Group C Blues
Southwest has an open seating policy. This is the source of much anxiety. If you are in Boarding Group A, you have your pick of the bins. If you are in Group C, you’re likely hunting for a sliver of space at the back of the plane while your seat is in row 4.
This creates a logistical nightmare. When the plane lands, you have to wait for everyone to get off before you can walk backward to get your bag.
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To avoid this, try these three things:
- Check in exactly 24 hours early. Set an alarm. Use a world clock.
- Pay for EarlyBird Check-In. It’s usually $15-$25. If you hate stress, it’s the best money you’ll ever spend.
- The "Under-Seat" backup. If you know you're Group C, pack your essentials (meds, chargers, headphones) in your personal item. That way, if your main bag gets gate-checked, you aren't digging through your underwear in the middle of the aisle to find your Kindle.
Real-world weight limits
Technically, Southwest doesn't have a published weight limit for carry-ons. As long as you can lift it over your head into the bin without assistance, you're usually fine.
But don't be that person.
The flight attendants are not required to lift your bag for you. In fact, many are instructed not to for worker's comp reasons. If you pack a 50-pound lead brick into a 24-inch suitcase, you better be ready to clean-and-jerk that thing into the bin yourself.
Actionable steps for your next flight
Don't leave your packing to the last minute. It leads to "over-packing bloat" where your bag expands like a pufferfish.
- Measure your bag at home with a tape measure. Do not trust the manufacturer. Measure from the floor to the top of the handle.
- Check your aircraft type. Look at your flight details on the Southwest app. If it says 737-700, the bins are smaller. Pack lighter. If it’s a MAX 8, you have more vertical room in the bins (they "drop down").
- Wear your heaviest items. If you're bringing a coat and boots, wear them on the plane. You can always take the coat off once you're in your seat. It saves massive amounts of volume in your carry on luggage Southwest setup.
- Consolidate before the gate. If you bought snacks or souvenirs in the terminal, shove them into your "one" personal item or carry-on. Having a bunch of loose plastic bags is a red flag for gate agents looking to trim the herd.
Buying a bag that is exactly $22 \times 14 \times 9$ is the safest bet for all airlines. But if you are a Southwest loyalist, finding that rare $24 \times 16 \times 10$ bag is like finding a cheat code for extra space. Just remember: the bigger the bag, the earlier you need to board. Space is a first-come, first-served commodity. Once it's gone, it's gone, and your bag is headed for the belly of the plane.