Southwest Personal Item & Carry-On — What Actually Fits
Will a 25L Backpack Fit on Southwest?
Southwest Airlines’ generous 24 × 16 × 10 inch carry-on allowance means a 25L backpack fits with a comfortable margin.
A 25L works well as a personal item on Southwest — though with checked bags no longer free on most fares (as of 2025), there's now more reason to keep your packing carry-on-friendly.
Placement: Personal Item (Under Seat)
Confidence: High
Best For: 1–3 Day Trips
Last updated: March 2026
Southwest allows 24 × 16 × 10 inches for carry-on bags — one of the most generous limits among major U.S. carriers. A 25L backpack fits this limit easily and will typically qualify as a personal item under the seat. Note that Southwest ended free checked bags on most fares in 2025, so carrying on now saves money it once didn't. This makes a compact 25L a flexible, fee-avoiding choice on Southwest.
Check if this will actually fit your trip →
Gear
Bags That Work on Southwest at 25L
Bags that work as a personal item on Southwest at 25L — based on real bag dimensions and under-seat fit.
Recommended Pick
Matein Travel Laptop Backpack
Personal-item friendly at 28L. Clears Southwest limits with a comfortable margin.
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Rolling alternative
Travelpro Maxlite 5 Compact Spinner
38L rolling carry-on at 22 × 14 × 9 in (55.9 × 35.6 × 22.9 cm). A structured alternative when a backpack isn't ideal.
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Stay Carry-On Only
This setup exceeds typical carry-on capacity. Add a personal item or check a bag.
Gear
Recommended Bags for This Trip
These recommendations are based on real bag dimensions compared to Southwest carry-on limits, plus how well each bag fits a 25-liter packing load.
Packing Reality Check
When Does a 25L Bag Work Well on Southwest?
Works Well
- As a personal item under the seat — fits comfortably on all Southwest 737s
- 1–3 day trips or as a companion to a free checked bag
- Travel where you check your main luggage and keep a daypack in-cabin
- Any Southwest fare — carry-on and checked bags included in every ticket
Becomes a Tight Fit
- Anything over 3 days as your only bag
- Cold-weather trips requiring jacket and layers
- Packing a laptop alongside full clothing rotation
- One-bag trips where you need volume — check a bag for free instead
Published Carry-On & Bag Limits
Southwest Carry-On Size Limits
| Max dimensions |
24 × 16 × 10 in61.0 × 40.6 × 25.4 cm |
| Weight limit |
No official carry-on weight limit; checked bags now cost a fee on most fares since 2025 |
| Personal item |
Yes — one personal item allowed (under seat) |
| Carry-on access |
Included on all fares; no additional fee |
| Fit at 25L |
A 25L backpack usually works as a personal item — slim designs fit under most seats; bulkier builds may need overhead |
For a full breakdown of size limits, boarding rules, and exceptions, see our airline carry-on rules guide →
Bottom Line
- On Southwest, a 25L bag uses the under-seat slot and leaves the 24 × 16 × 10 inch carry-on allotment open for a second bag
- Southwest's generous 24 × 16 × 10 inch limit makes 25L one of the easiest sizes to fly with
- Free carry-on plus personal item on every fare; checked bags now cost a fee on most fares (since 2025) — verify the current amount with Southwest
Airline enforcement
How Strict Is Southwest With Carry-On Bags?
Southwest is still one of the most forgiving U.S. airlines for carry-on bags. Every fare includes a carry-on plus a personal item at no charge, gate agents rarely measure carry-on bags, and the all-737 fleet has standardized overhead bins with no regional-jet complications. Weight limits aren't enforced on carry-on bags. The most common carry-on issue on Southwest isn't bag size — it's overhead space on full flights for C-group passengers. One important change: as of 2025, Southwest no longer includes free checked bags on most fares (standard fares now pay a checked-bag fee — verify the current amount with Southwest; free checked bags remain for A-List Preferred members, Choice Extra fares, Rapid Rewards cardholders, and military). That makes packing carry-on-only more valuable on Southwest than it used to be.
Size insight
25L Backpack on Southwest: What Actually Changes?
A 25L backpack is a comfortable personal item on Southwest. Southwest's personal item limit isn't strictly defined — it needs to fit under the seat. At 25L, virtually every bag design clears that bar. With checked bags no longer free on most fares (since 2025), there's more reason than before to pack efficiently. A 25L bag makes sense for 1–3 day trips or as a personal item alongside a carry-on — letting you skip checked-bag fees on shorter trips.
Notes
How Accurate Is This?
Southwest allows 24 × 16 × 10 inches (61.0 × 40.6 × 25.4 cm)—the largest carry-on dimensions among US domestic carriers. This extra space is a real advantage for 30–40L backpacks. Southwest's enforcement is the most relaxed in the US market; sizers are rarely deployed, and slightly oversized bags often pass without question.
Southwest used to be unique for including free checked bags, but that changed in 2025 — standard fares now pay checked-bag fees (verify the current amount with Southwest), with free bags only for A-List Preferred members, Choice Extra fares, Rapid Rewards cardholders, and military. So if your pack barely fits as a carry-on, checking it is no longer automatically free. Southwest's generous 24 × 16 × 10 in carry-on box still makes it one of the more backpacker-friendly U.S. airlines for carrying on, but the old "just check it for free" fallback now depends on your fare or status.
Southwest's boarding process (open seating, A/B/C groups) means earlier boarding groups secure better overhead bin space. Fly A or B boarding to minimize the risk that bins are full. Weight limits are never enforced on domestic flights.
This is a planning tool to estimate capacity; actual gate acceptance depends on agent discretion and time of year. Southwest's relaxed culture means a 30–40L bag is rarely controversial, even on fuller flights.
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