Southwest Airlines vs United Airlines Carry-On Size

You pack your usual carry-on, zip it up, and head to the airport without thinking twice. It worked on your last flight, so it should be fine again. But at the gate, things change. The same bag that fit easily on one airline suddenly doesn’t meet the size limit on another—and now you’re being asked to check it.

This confusion often happens when switching between airlines like Southwest and United. On paper, both offer carry-on baggage, but their luggage dimensions and enforcement can feel very different once you’re actually boarding.

Let’s break down Southwest Airlines vs United Airlines carry-on size so you know exactly what works and what doesn’t.

Southwest Airlines vs United Airlines Carry-On Size

Feature	Southwest Airlines	United Airlines
Carry-on size	61 x 41 x 25 cm	56 x 35 x 23 cm
	24 x 16 x 10 in	22 x 14 x 9 in
Personal item	Yes (1 item)	Yes (1 item)
Weight limit	Not specified	Not specified
Carry-on included	Yes	Yes (most fares)
Strictness level	Moderate	Moderate to Strict

Based on official airline policies

Southwest Airlines vs United Airlines Carry-On Size Comparison

This is where the biggest difference shows up right away.

Southwest Airlines

Southwest allows a carry-on size of:

• 61 x 41 x 25 cm (24 x 16 x 10 inches)

That’s noticeably larger than the standard cabin baggage size used by most airlines. You get more room in height, width, and depth, which means you can pack a slightly bigger suitcase or use expandable luggage without worrying too much.

United Airlines

United follows a more standard approach:

• 56 x 35 x 23 cm (22 x 14 x 9 inches)

These permitted dimensions are smaller across all sides compared to Southwest.

Key Difference

Southwest Airlines is clearly more flexible because it allows a larger carry-on size.

Even a few extra centimeters can matter, especially with:

• Hard-shell suitcases
• Fully packed bags
• Expandable luggage

Practical warning:
A bag accepted on Southwest may be rejected on United, especially if it exceeds that tighter width or depth.

Personal Item Rules Compared

This is another area where the two airlines take slightly different approaches.

Southwest Airlines

• 1 personal item allowed
• Size not officially specified
• Must fit under the seat

United Airlines

• Personal item size: 43 x 25 x 23 cm (17 x 10 x 9 inches)
• Clearly defined dimensions
• Must fit under the seat

What This Means in Real Life

United is more structured, while Southwest gives more flexibility.

Example:

• A compact laptop bag → accepted on both
• A medium-sized backpack → likely fine on Southwest
• The same backpack → may be questioned on United if it exceeds their size restrictions

If your bag looks bulky, both airlines can treat it as a carry-on instead of a personal item.

Weight Limits & Baggage Allowance

Both airlines follow a similar pattern here.

Southwest Airlines

• No published weight limit
• You must lift your bag yourself

United Airlines

• No official weight restriction
• Same expectation: self-handling

Key Insight

This is typical for U.S. airlines.

Unlike many international carriers:

• Weight checks are rare
• Size rules are more important

Important tip:
If you’re connecting to an international airline, you may suddenly face strict weight limits—even if your first flight didn’t check.

Carry-On Fees Comparison

This is where Southwest has a clear advantage.

Southwest Airlines

• 1 carry-on + 1 personal item included
• No extra cost for cabin baggage

United Airlines

• Carry-on included in most fares
• Basic Economy may not include a full carry-on

Key Difference

Southwest is more straightforward—everyone gets a carry-on.

United can vary depending on fare type.

Practical tip:
If you book a cheaper United ticket, double-check your baggage allowance before arriving at the airport.

Which Airline Is More Strict?

Rules on paper are one thing. What happens at the gate can be different.

Southwest Airlines

• Rarely enforces size aggressively
• Focuses on fast boarding
• Less emphasis on measuring bags

United Airlines

• More structured boarding process
• Greater chance of size checks
• More consistent enforcement

Verdict on Strictness

Based on traveler experience:

• Southwest feels more relaxed
• United is stricter in real-world enforcement

This becomes more noticeable on full flights where overhead space is limited.

Real Travel Scenarios

Here’s how these differences play out in real situations.

Scenario 1: Same Bag on Both Airlines

You use a slightly oversized carry-on:

• Works fine on Southwest
• May be stopped on United

Even a small difference in dimensions can affect acceptance.

Scenario 2: Backpack vs Suitcase

You carry:

• Cabin suitcase + backpack

On Southwest:

• Backpack usually accepted as personal item

On United:

• Backpack must fit within defined size

If it’s too big, it may count as a second carry-on.

Scenario 3: Connecting Flights

You fly:

• Southwest → United

Your bag:

• Accepted on Southwest
• Exceeds United’s permitted dimensions

Warning:
Always follow the stricter airline when flying multiple segments.

Which Airline Is Better for Carry-On?

Let’s break it down clearly.

Best for Flexibility: Southwest Airlines

Southwest Airlines is slightly more flexible because it allows larger luggage dimensions and doesn’t strictly define personal item size.

Best for Structure: United Airlines

United provides clear size restrictions, which helps travelers know exactly what’s allowed.

Best for Budget Travelers: Southwest Airlines

Carry-on is always included, with no fare-based restrictions.

Best Overall

Southwest Airlines wins due to its larger carry-on allowance and more relaxed enforcement.

Related Airline Rules

• Southwest Airlines carry-on size guide
• United Airlines carry-on rules
• Carry-on vs personal item explained
• Carry-on weight limits guide

Traveler Insight (Not Official Policy)

From experience, Southwest boarding feels more relaxed. Staff rarely focus on exact measurements unless a bag looks obviously oversized. Since seating is open, passengers spread out, which often leaves more room for cabin baggage.

United operates differently. Boarding groups are tighter, and overhead space fills quickly. On busy flights, gate agents are more likely to check bags that look even slightly larger than the permitted dimensions.

Another thing I’ve noticed is that United flights tend to run out of overhead space faster. When that happens, even compliant bags may be gate-checked, especially for later boarding groups.

FAQs

Which airline allows bigger carry-on?

Southwest Airlines allows a larger carry-on size than United.

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Can I use the same bag on both airlines?

Yes, but it should meet United’s smaller size limit to be safe.

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What happens if my bag is oversized?

You may need to check it at the gate, and additional charges may apply.

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Do both airlines allow personal item?

Yes, both allow one personal item.

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Are carry-ons included in fare?

Southwest includes it for all passengers. United includes it in most fares, but not all.

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Final Verdict

Data verified from official airline baggage policies.

If you want to stay safe across both airlines, stick to United’s smaller size limit. But if you’re flying Southwest, you’ll have more room to pack—and fewer chances of being stopped at the gate.