Bag sizes
Personal item size: which backpack goes free under the seat?
Type the three sides of your backpack or tote: the checker lists the airlines whose under-seat limit it meets, and the side that is too long where it does not.
Will my bag fit? Your bag against 9 airlines
Fits as a personal item (under the seat)
4 of 5 airlines
- American AirlinesFits (18 × 14 × 8 in)
- Delta Air LinesNo published limit
- United Airlines2.0 in too big (17 × 10 × 9 in)
- Southwest AirlinesNo published limit
- Alaska AirlinesNo published limit
- JetBlueFits (17 × 13 × 8 in)
- Frontier AirlinesFits (18 × 14 × 8 in)
- Allegiant AirFits (18 × 14 × 8 in)
- Hawaiian AirlinesNo published limit
A personal item is the small bag that rides under the seat in front of you, and it is free on every fare of every US airline on this site. The size is not the same everywhere. American, Frontier and Allegiant publish 18 × 14 × 8 in (46 × 36 × 20 cm). United is the strictest at 17 × 10 × 9 in (43 × 25 × 23 cm), and JetBlue prints 17 × 13 × 8 in (43 × 33 × 20 cm) in its terms. Delta, Southwest, Alaska and Hawaiian give no number at all: their rule is only that the bag must fit under the seat. Frontier is the one airline that also weighs it, with a cap of 35 lb (15.9 kg). In practice a backpack of 17 by 10 by 9 inches passes on every airline that publishes a size, which is why travelers on cheap fares choose that format. A bag that is larger but soft can still be accepted if it squeezes into the sizer, while a rigid case of the same outside size cannot.
Personal item or carry-on: how much more space?
Carry-on space vs personal item
1.4 times
| Personal item | about 33 liters |
| Carry-on | about 46 liters |
| Carry-on on the lowest fare | included |
Volume of the largest box allowed; soft bags rarely fill it.
Sizes, fees and rules read by Radif Partners · Editorial policy · How we check
Under-seat limits published by each US airline
Five airlines print a size. The table quotes it as written on the airline's page, with our conversion in brackets. Where an airline publishes no size, the only test is the space under the seat on your aircraft, which varies by seat row and aircraft type.
| Airline | Personal item | Weight |
|---|---|---|
| American Airlines | 18 × 14 × 8 in (46 × 36 × 20 cm) | none stated |
| Delta Air Lines | no size published, must fit under the seat | none stated |
| United Airlines | 17 × 10 × 9 in (43 × 25 × 23 cm) | none stated |
| Southwest Airlines | no size published, must fit under the seat | none stated |
| Alaska Airlines | no size published, must fit under the seat | none stated |
| JetBlue | 17 × 13 × 8 in (43 × 33 × 20 cm) | none stated |
| Frontier Airlines | 18 × 14 × 8 in (46 × 36 × 20 cm) | 35 lb (15.9 kg) |
| Allegiant Air | 18 × 14 × 8 in (46 × 36 × 20 cm) | none stated |
| Hawaiian Airlines | no size published, must fit under the seat | none stated |
Why United's number is the one to pack for
United allows 17 × 10 × 9 in (43 × 25 × 23 cm), the smallest depth and width of the group. It is also the airline where the size matters most, because Basic Economy passengers on most domestic routes travel with the personal item alone. A bag built for 18 × 14 × 8 in (46 × 36 × 20 cm) is two inches too long for United's 17-inch side and four inches too wide on the 10-inch side. Backpacks sold as "personal item size" are often built around one airline; the checker above compares yours against all of them in one go.
How much fits in a personal item
A box of 17 × 10 × 9 in (43 × 25 × 23 cm) holds about 25 liters; the American and Allegiant box about 33. That is enough for two or three days of clothes rolled tightly, a toilet bag of small containers and a laptop. The tool below gives the ratio between the personal item and the carry-on for each airline, which helps decide whether paying for the larger bag is worth it.
Personal item or carry-on: how much more space?
Carry-on space vs personal item
1.4 times
| Personal item | about 33 liters |
| Carry-on | about 46 liters |
| Carry-on on the lowest fare | included |
Volume of the largest box allowed; soft bags rarely fill it.
Low-cost airlines check it at the door
On Frontier and Allegiant the personal item is the only free bag. Allegiant publishes 18 × 14 × 8 in (46 × 36 × 20 cm) and sells the carry-on separately; Frontier adds its weight cap. Both airlines charge more for a bag paid at the airport than for one added at booking, so a backpack that fails the sizer is the most expensive way to travel with it. Pack it, close it and measure it the night before, including side pockets with a water bottle.
Flying in Europe with the same bag
UK and European airlines publish the under-seat bag in centimetres, at 40 × 30 × 20 cm (15.7 × 11.8 × 7.9 in) on Ryanair and 40 × 30 × 15 cm (15.7 × 11.8 × 5.9 in) on British Airways. A US personal item of 18 by 14 by 8 inches is 46 by 36 by 20 cm, too long for both. The under-seat bag page covers the UK sizes in detail.