Personal Item Size by Airline: What Fits Under the Seat
Every US airline lets you bring one personal item for free, even on the cheapest fare. The size they allow is not the same, and the budget airlines check. Here is how the limits compare and how to buy a bag that passes.
The published limits
Airlines change these numbers, so treat this as a starting point and confirm on the airline's own site before you fly.
- American Airlines: 18 x 14 x 8 inches. Strict on the 8-inch depth.
- Spirit and Frontier: 18 x 14 x 8 inches, and both are known for using the sizer at the gate and charging for bags that do not fit.
- United: 17 x 10 x 9 inches, the smallest common limit. Basic Economy passengers are held to it.
- Southwest: a smaller figure than the 18 x 14 x 8 standard; check the current number on its site.
- Delta: publishes no fixed dimensions and requires the item to fit under the seat in front of you.
The practical rule: a bag that genuinely measures 18 x 14 x 8 when packed passes American, Spirit and Frontier. For United, you need a smaller bag or a lightly packed one.
Why "when packed" is the whole game
Soft backpacks are measured empty by the maker and full by the gate agent. Some listings are honest about this and give two sizes, such as 16.5 x 11.8 x 7.1 inches empty and 18 x 14 x 8 loaded. That second number is the one that matters, and it also means the bag has no spare room: overpack it and it fails.
Depth is where most bags fail. Keep the packed depth under 8 inches, close any expansion zip, and tighten compression straps if the bag has them.
Features that help at the gate
- A suitcase-style 180-degree opening lets you repack quickly if you are asked to.
- Compression straps pull a half-full bag back to shape.
- A luggage pass-through strap keeps the bag on your roller through the terminal so you are not tempted to overfill it.
- An expandable bag gives you both sizes, as long as you remember which flight is which.
Bags from our comparison
From the listings we compared: the fixed-size ZOMFELT and the expandable ZOMFELT both state 18 x 14 x 8 inches; the Lossga reaches that size when loaded; the Sinaliy is 16.9 x 11.8 x 7.9 and the HILOMON 17.1 x 11.5 x 7.1, which gives those two the best chance on airlines with tighter sizers.
One more thing
Weight limits on personal items are rare in the US but common abroad. If your trip includes a European or Asian carrier, check for a kilogram limit as well as the dimensions.