ULCC Personal Item Sizes: Frontier, Allegiant, and United (2026)
On official pages fetched November 10, 2026, Frontier’s free personal item is 18 × 14 × 8 in, including handles, wheels and straps, up to 35 lb, and must fit under the seat. Allegiant’s free personal item is 8 × 14 × 18 in (20 × 35 × 45 cm), also including wheels, pockets, handles and decorations, and must fit under the seat. United’s personal item is a tighter 9 × 10 × 17 in under-seat box. We could not retrieve official Spirit Airlines bag pages in this environment, so Spirit sizes are not cited here. This is an under-seat guide, not an overhead carry-on guide.
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How this page was made: this is a research-based guide built from manufacturer spec pages, official prices and published lab measurements from the outlets we name and link. We haven’t tested these products ourselves, and we don’t invent scores. Our methodology.
Quick answer
On official pages fetched November 10, 2026, Frontier’s free personal item is 18 × 14 × 8 in, including handles, wheels and straps, up to 35 lb, and must fit under the seat. United’s personal item is a tighter 9 × 10 × 17 in under-seat box.
Last updated Prices checked Nov 10, 2026
We fetched official bag pages from Frontier, Allegiant, and United on November 10, 2026, and compared those published personal-item boxes with official dimensions already sourced for Away’s Everywhere Bag, the Monos Metro Duffel, and BÉIS’s Mini Weekender. We have not put these bags in an airport sizer, and we do not invent scores. Official Spirit Airlines support and contract-of-carriage pages returned errors from this environment (HTTP 500 or failed TLS), so we are holding Spirit-specific sizes rather than quoting search snippets. Confirm the live rule for your airline and fare at booking, and measure your packed bag, including handles, wheels, straps, pockets, and decorations where the airline says those count.
For bag-by-bag picks against Frontier and United, see best personal item bag. For overhead carry-ons on the same airlines, see best carry-on for budget airlines. Those are different boxes.
Official personal-item boxes, side by side
| Frontier | Allegiant | United | |
|---|---|---|---|
| Published personal-item size | 18 × 14 × 8 in, up to 35 lb | 8 × 14 × 18 in (20 × 35 × 45 cm) | 9 × 10 × 17 in (22 × 25 × 43 cm) |
| What is included in the measurement | Handles, wheels and straps, as written on the bag-options page | Wheels, pockets, handles and decorations | The page states the item must fit under the seat in front of you at 9 × 10 × 17 in. It does not use Frontier’s “handles, wheels and straps” sentence on that size line; measure conservatively. |
| Where it must fit | Under the seat. Frontier says size will be checked at boarding, and oversized items can be charged. | Under the seat. An oversized personal item may be treated as a paid carry-on. | Under the seat. Small purses or bags are not allowed in addition to the personal item and carry-on. |
| How this differs from a carry-on | A paid carry-on is a different 24 × 16 × 10 in box, up to 35 lb, for the overhead bin. | A paid carry-on is 10 × 16 × 22 in (25 × 40 × 55 cm) for the overhead bin, with the same measurement rule. | A carry-on is 9 × 14 × 22 in including the handle and wheels, for the overhead bin. Basic Economy is usually a personal item only, with a fee change for tickets purchased on or after April 3, 2026. |
Frontier and Allegiant publish boxes that are close in overall volume — both use an 18-inch long side and an 8- or 14-inch pairing — but they write the dimensions in a different order, and Allegiant explicitly counts pockets and decorations. United’s 9 × 10 × 17 in box is meaningfully tighter on two sides. A bag that sits inside Frontier’s published box can still sit over United’s 9 in or 10 in sides. That is why the same soft bag can be a clean personal item on one itinerary and a problem on a connecting United segment.
Allegiant’s baggage page we fetched also notes that its contract of carriage applies to travel on or after July 21, 2026, and that airport fees can be higher than fees paid in advance. We did not fetch a current official Allegiant fee table with dollar amounts in this pass, so we are not quoting carry-on or oversized fees here.
How three official bags sit in those boxes
These are the official empty or listed sizes from each brand, compared with the published airline boxes. Packed bags can measure larger. Brand pages do not always say whether straps and handles are included in the spec.
| Bag | Official size / price | Vs Frontier 18 × 14 × 8 in | Vs Allegiant 8 × 14 × 18 in | Vs United 9 × 10 × 17 in |
|---|---|---|---|---|
| Away The Everywhere Bag | 16.3 × 10.2 × 7.3 in; 20 L; $198. The page does not say whether straps and handles are included. | All three official numbers sit inside the published box. | All three official numbers sit inside the published box (10.2 sits under 14; 7.3 under 8; 16.3 under 18). | 10.2 in is slightly over the published 10 in; 16.3 in fits 17 in; 7.3 in fits 9 in. |
| Monos Metro Duffel | 11.2 × 16.3 × 7.2 in without the Metro Kit; 19.6 L; $225. The page does not say whether the strap is included. | All three official bag numbers sit inside the published box. Measure again if the Metro Kit is clipped on. | All three official bag numbers sit inside the published box (11.2 under 14; 7.2 under 8; 16.3 under 18). | 11.2 in is over both the published 9 in and 10 in; 16.3 in fits 17 in; 7.2 in fits 9 in. |
| BÉIS The Mini Weekender | 16.14 × 15.75 × 7.87 in; 32 L; $108. A compare block on the same site also lists 7.8 in depth. | 15.75 in height is over Frontier’s published 14 in. | 15.75 in is over Allegiant’s published 14 in on that side. | 15.75 in and 16.14 in are over United’s 9 in, 10 in, and would only be judged against the 17 in side if turned — still over on the other sides as written. |
Away says the Everywhere Bag “meets the airline requirement as a personal item” without naming an airline. BÉIS markets the Mini Weekender as a personal item, but the official height is over Frontier’s and Allegiant’s published 14 in sides. We report the numbers, not the marketing line. For the full warranty and return terms on these three bags, use best personal item bag.
Why Spirit sizes are held
This guide would be more useful with Spirit’s official personal-item box, because Spirit is one of the U.S. ultra-low-cost carriers people actually fly with Frontier and Allegiant. Official Spirit support articles and the contract-of-carriage PDF could not be retrieved here on November 10, 2026 (support pages returned HTTP 500; other official hosts failed TLS or returned an error page instead of the PDF). We are not filling that gap from search snippets. If you are flying Spirit, use the airline’s current bag page or contract of carriage, and measure the packed bag against the sizer at the airport.
Who should skip this guide
- Travelers shopping for an overhead carry-on. Use best carry-on for budget airlines. Frontier’s 24 × 16 × 10 in and Allegiant’s 10 × 16 × 22 in carry-on boxes are not personal-item sizes.
- Readers who only need Frontier versus United bag picks. Best personal item bag already covers those two airlines in more product detail.
- Anyone flying Spirit who needs a cited official Spirit size. We held those figures until an official page can be fetched.
- Passengers who want a fee quote. We did not fetch a current official Allegiant dollar fee table in this pass, and fare rules change by ticket date.
Frequently asked questions
Is Frontier’s personal item the same size as Allegiant’s?
Will a bag that fits Frontier also fit United?
Does the BÉIS Mini Weekender fit these ULCC personal-item boxes?
Why isn’t Spirit in the table?
Is a personal item the same as a carry-on on these airlines?
Sources
Pricing and plan details were checked on the official pages below as of Nov 10, 2026. Vendors change prices, credits and plan names often, and some show regional pricing at checkout, so confirm on the vendor’s site before you buy.
- Frontier Airlines: Bag Options — personal item 18 × 14 × 8 in including handles, wheels and straps, up to 35 lb; carry-on 24 × 16 × 10 in (fetched Nov 10, 2026) (flyfrontier.com)
- Allegiant Air: Baggage — personal item 8 × 14 × 18 in including wheels, pockets, handles and decorations; carry-on 10 × 16 × 22 in; contract on/after July 21, 2026 (fetched Nov 10, 2026) (allegiantair.com)
- United Airlines: Carry-on bags — personal item 9 × 10 × 17 in; carry-on 9 × 14 × 22 in including handle and wheels; Basic Economy note and April 3, 2026 fee change (fetched Nov 10, 2026) (united.com)
- Away: The Everywhere Bag (Jet Black) official product page — $198, 16.3 × 10.2 × 7.3 in, 20 L (fetched Nov 10, 2026) (awaytravel.com)
- Monos: Metro Duffel official product page — $225, 11.2 × 16.3 × 7.2 in, 19.6 L (fetched Nov 10, 2026) (monos.com)
- BÉIS: The Mini Weekender official product page — $108, 16.14 × 15.75 × 7.87 in, 32 L (fetched Nov 10, 2026) (beistravel.com)
Related
The Best Personal Item Bag for Holiday Flights
If you need a bag that sits inside Frontier’s published 18 × 14 × 8 in personal-item box (handles, wheels and straps included), the official dimensions for Away’s Everywhere Bag and the Monos Metro Duffel do. BÉIS’s Mini Weekender lists more capacity, but its 15.75 in height is over Frontier’s published 14 in limit — and all three official sizes sit over United’s tighter 9 × 10 × 17 in box on at least one side.
best ofBest Carry-On for Budget Airlines (2026)
This is a size guide, not a ranked test. On official pages fetched November 10, 2026, Frontier’s carry-on is 24 × 16 × 10 in (up to 35 lb), Allegiant’s is 10 × 16 × 22 in, and United’s is 9 × 14 × 22 in including the handle and wheels. Monos’ Carry-On lists 22 × 14 × 9 in at $275, which sits inside all three published boxes. Away’s Carry-On lists 22 × 14.4 × 9.1 in at $275 — inside Frontier and Allegiant, over United’s 14 in width. Briggs & Riley’s Baseline Essential 22" lists 22 × 14 × 9 in unexpanded at $679, and 11.5 in deep when expanded. Spirit official bag pages could not be fetched here, so Spirit sizes are not cited.
guideWeekender vs Carry-On (2026)
Choose a weekender duffel if you want a lighter soft bag you can shoulder or stack on a roller — Away’s Weekender is $248, 38 L, and 3.8 lb with the strap, but Away’s own FAQ says it is not a personal item and is too large under a seat when fully packed. Choose a wheeled carry-on if you want a structured spinner with a built-in lock and a suitcase warranty; Away’s Carry-On is $275 and about twice the empty weight, with official size figures that conflict across Away’s own pages. Confirm the packed bag in a sizer. United’s published limit is 9 × 14 × 22 inches including handles and wheels.
best ofTSA 3-1-1 Toiletry Kits and Travel Bottles, Explained (2026)
TSA’s official liquids rule is a quart-sized clear plastic zip-top bag, containers of 3.4 ounces (100 milliliters) or less, and one bag per passenger. A branded clear toiletry case is not automatically that bag. On official pages fetched November 10, 2026, Away’s Clear Toiletry Bag is $75 and 8.3 × 5.5 × 3.6 in — useful as a clear organizer, not a claimed quart 3-1-1 substitute. Matador’s FlatPak bottle is $15; the same page says both 3 fl oz (100 mL) and a 3 oz (90 mL) volume. Cadence’s Large Capsule is $38 and 2.75 fl oz, with a stated fit of four in a quart-sized bag.