The best underseat carry-on bags
When the personal item is the only bag you get, the under-seat envelope becomes the whole specification. These clear it - and one of them clears United's, which most do not.
By Michael W. · Last updated September 28, 2026
We earn a commission when you buy through our links, at no extra cost to you. It never changes what we pick or how we rank it. How we’re funded.
The under-seat bag used to be an afterthought - the laptop sleeve you carried alongside your real luggage. Basic Economy changed that. On United and Delta's cheapest domestic fares, and on most Frontier and Spirit fares, the personal item is the entire free baggage allowance. The bag at your feet is now the bag.
Which makes the specification unusually precise, because the airlines publish it. American, Frontier and Spirit all state 18 x 14 x 8 inches. JetBlue states 17 x 13 x 8. United states 17 x 10 x 9 - the tightest figure of the major carriers, and the one that rules out most bags sold as 'personal item' bags. Delta, Southwest and Alaska publish nothing at all. Full detail in personal item size by airline.
Quick picks
The short list. Tap any row for the full write-up, including what each one is bad at.
| # | Product | Best for | Price |
|---|---|---|---|
| 1 |  Cotopaxi Allpa 35L Travel Pack Clamshell opening and a square profile that fills the 18 x 14 x 8 envelope properly. | American, Frontier and Spirit | |
| 2 |  Osprey Daylite Plus Daypack Slim enough for the tightest published personal item limit in the US. | United Basic Economy | |
| 3 |  Patagonia Black Hole Duffel 25L Frameless, so it becomes whatever shape the under-seat space happens to be. | Delta, Southwest and Alaska | |
| 4 |  Samsonite Wheeled Underseater Rolls to the gate and still fits under the seat once you are on board. | Long terminals, bad backs | |
| 5 |  Narwey Foldable Travel Duffel Bag Packs flat inside your main bag, opens up when the personal item is all you get. | Occasional Basic Economy fares |
The one that makes the under-seat allowance feel like real luggage
Cotopaxi Allpa 35L Travel Pack
If your airline publishes 18 x 14 x 8, the winning bag is the one that fills that box rather than approximating it. A clamshell pack opens flat like a suitcase, which is the difference between being able to find something while it is wedged under a seat and having to haul it out into the aisle.
The specs that decide it
- Fits: The 18 x 14 x 8 envelope published by American, Frontier and Spirit
- Opening: Clamshell - full access without unpacking from the top down
- Does not fit: United's published 17 x 10 x 9, on depth and width
Flaws but not dealbreakers
Over United's published personal item limit, which is a real problem given United Basic Economy is one of the main reasons to buy a bag like this. Fully loaded it is also heavy to push under a seat with your foot, which is how you will actually be doing it.
The one that actually clears United's 17 x 10 x 9
Osprey Daylite Plus Daypack
United's 10-inch width is what eliminates most of this category, and it is also the airline where the personal item matters most, because Basic Economy strips the carry-on out. A slim daypack clears it. If United is your main carrier, buying an '18x14x8 personal item bag' is buying the wrong bag, however it is marketed.
The specs that decide it
- Fits: United's 17 x 10 x 9, and therefore every other carrier in our table
- Shape: Slim profile - width is the dimension that decides this one
- Compresses: Soft build squashes into a sizer under a firm push
Flaws but not dealbreakers
Modest capacity, and on carriers with a generous 18 x 14 x 8 allowance you are leaving free space unused. It is a daypack rather than a travel pack, so there is no clamshell access and no dedicated packing organization.
The one for airlines that publish no dimensions at all
Patagonia Black Hole Duffel 25L
Delta, Southwest and Alaska publish no personal item figure - the rule is simply that the bag fits under the seat. A frameless soft duffel is the right answer to that ambiguity: nothing rigid to object to, and it compresses into whatever space actually exists, which varies between window and aisle seats more than most people realize.
The specs that decide it
- Best for: The three carriers that publish no personal item dimension
- Structure: Frameless - compresses to the space available
- Fabric: Coated, so a wet walk to the terminal is not a problem
Flaws but not dealbreakers
No structure means no organization. Everything migrates to the bottom, finding one item means unpacking several, and there is no laptop protection unless you add a sleeve. It is a good bag and a poor office.
The one for people who should not be carrying weight
Samsonite Wheeled Underseater
A wheeled under-seater is a niche product that solves a real problem: if you cannot comfortably carry a loaded bag across a long terminal, the whole 'just use a backpack' answer does not apply to you. These are sized to slide under a seat with the wheels included, which is the part cheap versions get wrong.
The specs that decide it
- Fits: Designed to the under-seat envelope with wheels counted
- Access: Front pocket for laptop and documents without opening the main bag
- Why: Removes the carry entirely, which matters more than it sounds
Flaws but not dealbreakers
The wheels and handle eat capacity from a bag that has very little to spare, so you get noticeably less usable space than a soft bag of the same external size. Wheeled under-seaters are also heavier empty than everything else on this list.
The one that costs almost nothing and folds away when you are done
Narwey Foldable Travel Duffel Bag
If Basic Economy is an occasional thing rather than how you always fly, spending real money on a dedicated under-seat bag makes little sense. A foldable duffel lives inside your normal luggage taking up no space, and comes out for the flights where it is needed.
The specs that decide it
- Fits: Soft-sided - compresses into the under-seat space on any carrier
- Storage: Folds flat when empty
- Cost: The cheapest solution to the personal item allowance
Flaws but not dealbreakers
Thin fabric and no structure. It will not survive being used as an everyday bag, there is no padding for electronics, and a full one is uncomfortable to carry because the handles dig in.
How they compare
| Pick | Type | Clears 18 x 14 x 8? | Clears United 17 x 10 x 9? | Main flaw |
|---|---|---|---|---|
| Cotopaxi Allpa 35L | Clamshell pack | Yes | No | Heavy when full |
| Osprey Daylite Plus | Slim daypack | Yes | Yes | Modest capacity |
| Patagonia Black Hole 25L | Soft duffel | Yes | Compresses to fit | No organization |
| Samsonite wheeled underseater | Wheeled bag | Yes | Check the model's stated size | Wheels eat capacity |
| Narwey foldable duffel | Foldable duffel | Yes | Compresses to fit | Thin fabric, no padding |
Who this list is for
Anyone flying a fare where the personal item is the only free bag: United or Delta Basic Economy on most domestic routes, or a standard Frontier or Spirit fare. It is also for people who fly full-service fares and want the under-seat bag to be a genuine second bag rather than a laptop sleeve - which, on an airline publishing 18 x 14 x 8, it easily can be.
If you have a full carry-on allowance and just want something small for the seat pocket essentials, this is more bag than you need - long-haul flight essentials is the more useful page.
The United problem, stated plainly
United publishes 17 x 10 x 9 inches for the personal item. The 10-inch width is the killer: an 18 x 14 x 8 bag is four inches too wide, which is not a rounding error and not something a firm push into a sizer will solve.
This matters because a large share of bags marketed as 'personal item bags' are built to 18 x 14 x 8 and sold as universal. They are not. If United is your main carrier, check the width first and ignore everything else about the listing until it passes. The full figures for every carrier are in personal item size by airline.
Under-seat space is not uniform
The space under a window seat is often narrower than under a middle or aisle seat because of entertainment or power boxes mounted on some aircraft. Bulkhead rows frequently have no under-seat space at all - everything goes overhead for takeoff and landing. If you are relying on a large personal item, avoid the bulkhead.
How we chose these picks
The first filter was fit against published dimensions, because on this category that is not a preference, it is the entire specification. After that: access - can you reach things while the bag is under a seat, which rules out most top-loading designs; weight when loaded, because you will be pushing it into place with a foot; and whether the bag compresses, which is what saves you at a strict gate.
We have not measured these bags ourselves against a gate sizer. The dimensions above are the manufacturers' stated figures checked against the airlines' published limits. Our methodology sets out what we do and do not verify.
What we passed over
- Expandable personal item bags. The expansion takes them over the limit, which defeats the purpose on the exact fares where you need the bag.
- Bags marketed as '18x14x8 universal'. That figure is not universal - it fails United's published limit on two dimensions.
- Hard-sided under-seat cases. Rigid construction cannot compress into the varying space under different seats, and gives up capacity to the shell.
- Anything with external water bottle pockets that protrude. They count toward the measurement and they are the first thing a sizer catches.
How to choose an under-seat bag
- Look up your airline's published figure first. If it publishes one, that is the specification. If it publishes none - Delta, Southwest, Alaska - stay inside 18 x 14 x 8 and nothing will refuse you.
- Check width before anything else if you fly United. Ten inches. It is the dimension that eliminates most of the category.
- Prefer a clamshell or front-access design. Under-seat bags are used while they are under a seat. Top-loaders do not work there.
- Choose soft over rigid. Compression is what saves you when the sizer is being used, and rigid shells give up interior space to structure you do not need.
- Keep the weight down. You will be pushing this into place with your foot in a confined space, repeatedly.
Frequently asked questions
What size bag fits under an airplane seat?
Does a personal item bag fit on every airline?
Can I bring an underseat bag and a carry-on?
Is a backpack allowed as a personal item?
Are wheeled underseat bags worth it?
Read next
- Personal item size by airline
- Best personal item bags
- Best carry-on luggage
- Long-haul flight essentials
- Best packing cubes
More in Luggage, or see every roundup and comparison on the site.