Underseat Backpack Dimensions That Consistently Clear International Personal Item Rules

There is no one-size-fits-all personal item size; the smallest size in your travel class may also be the best number to plan for. Lufthansa accepts 40 x 30 x 15 cm, for example, regardless of travel class, United allows for 9 x 10 x 17 in on all classes, LATAM allows for up to 45 x 35 x 20 cm, including pockets, wheels, and handles.

This is only one part of the equation. The limit listed for personal items is the maximum allowable size as chosen by the airline, while the area under your seat is a space that can vary from one aircraft to another, sometimes even between different cabins, and sometimes even between different seats in the same plane. For example, Delta says the floor space available under the seat in a main-cabin A350-900 is approximately 14 x 15 x 8.8 in. Under a 767-300ER seat, it is much smaller, around 10 x 12 x 9 in.; in certain areas of the business cabin, there may be no space under the seats. Your backpack may meet the maximum allowable size under the personal item policy, but due to variations in the airplane’s configuration/space under your seat, you might not be able to fit it under the seat.

There Is No Universal Underseat Standard Behind Personal Item Size

The allowances provided on each carrier’s website were only read on 20 September 2026, so each airline may change their figures without notice. Therefore, the only web page that has the correct information for your particular flight is the one provided by your airline. This is even more important in this area of travel, as the agency everyone considers to be in charge of air travel has stated that it is not.

The numbers do not come from security screening. When directly asked about the size limits for carry-on items, the TSA indicates that bag dimensions “vary between airlines” and recommends contacting the airline for guidance in terms of overhead bin and seat space. In the United States, there is no federal regulation that indicates a maximum size for personal items, e.g. the 45 x 35 x 20 cm limit is a commercial policy developed by each airline and is subject to change.

So the spread is real, and it is wider than the round figures suggest:

Many people forget that the depth limitation of Lufthansa’s 15 cm is one of the most significant factors. An item that meets LATAM’s carry-on limit of 20 cm depth will exceed Lufthansa’s maximum depth by 5 cm before anything is packed into it, and a passenger travelling on a two-airline itinerary must abide by the regulations of the airline with the stricter limit.

This is also where it is no longer safe to rely exclusively on aggregated “personal item dimensions for airlines” charts. Often, these tables will fall out of date quietly; for example, at least one very popular luggage manufacturers’ chart still has a Lufthansa personal item dimension that is not consistent with the published information provided by Lufthansa. Refer to the respective airline’s luggage page for each of the airlines represented by your tickets, and use every chart, including this chart, as a guide and not a final authority.

Your Airline’s Personal Item Allowance Is Not the Space Under the Seat

An allowance is a means of providing an answer to a commercial dilemma about how much cabin baggage an airline will sell to you for the price you paid. It represents the maximum cabin baggage size as determined by the airline and does not define the amount of cabin baggage that will fit in the physical space available in the aircraft. Consequently, an established allowance does not guarantee that any bag at the maximum size designation will fit in the floor space at your seat.

The basis for the regulation regarding cabin stowage is very clear. Under 14 CFR 121.589, a US carrier is not allowed to permit a passenger to board if they have carry-on baggage unless all items in that baggage have been placed into a location designated by the carrier, which includes where the baggage will ultimately be stored, and not what the airline has declared as the maximum size for it to be stored in. Examples of locations approved for stowage include the overhead bin, a closet and under the seat. The carrier is the one responsible for ensuring that the passenger’s items are stored legally prior to the aircraft being pushed back from the gate.

It is this disconnect between the airline’s number and the physical space available for stowage on the aircraft that is the core of the issue. The airline’s page describes to you a number that the carrier will accept, while the aircraft describes a cavity. The two numbers are not calculated off of one another, nor are they established by the same entity. The airline’s stated personal item allowance of 45 x 35 x 20 cm for carry-on baggage on the same flight as a 25 cm depth under-the-seat opening is an example of how both allowances can coexist on the same flight without errors, and in any given instance of the two having a relationship together, it is the cavity that ultimately prevails.

In real-world terms, this means that for a compliant carry-on bag, there are two separate evaluations that must be passed, and most packing advice only discusses the first, the compliance with the personal item allowance. The second evaluation, which determines if the bag will actually fit beneath the seat, is the one that really matters.

What Actually Occupies the Space Under an Airline Seat

Underneath each airline seat lay not only empty rectangle floor areas, but the structure of the individual seats and whatever airline equipment is attached to them is the actual interruption in the floor space, creating an asymmetrical arrangement that is not necessarily equal from one seat to another.

In-flight entertainment (IFE) equipment has become the most common equipment obstruction. All long-haul commercial aircraft equipped with IFE units will typically have the processing units located beneath the seat in a metal enclosure bolted to the aircraft floor. Normally, these units are located directly below one or two of the three seats within a seat block and not the entire seat block. The enclosure limits the amount of space that can be used by the passenger seated behind the IFE unit, as the enclosure will reduce usable width and usable height by several centimeters. Additionally, the foot support legs for the seats and the horizontal structural connector that connects the legs to each of the seats intrudes into the usable space. As a result, it is typical for the usable opening for the passenger to be narrower at the bottom than the opening that the passenger sees when looking down on the seat. Thus, the airline’s published measurement for a seat is only a generalization based on the seating position and not necessarily an accurate measurement for your seat.

Actual measurements of the usable dimensions of the area under each seat have been taken by the Dog Jaunt organization as part of the “Dog Jaunt Under-seat Measurement Project“. Data from this long-standing project and other studies have consistently shown that the IFE equipment boxes will vary in size and height from one aircraft type to another and from row to row on the same type of aircraft. On several narrow-body types, the window, middle, and aisle seats will have different usable dimensions; the middle seat is typically where IFE equipment will be located.

On a practical note, the width of a backpack is typically the limiting factor more so than its height. A standard soft pack will compress vertically when moderate forces are applied. A soft pack cannot compress past a steel IFE housing or a seat leg. Therefore, if a backpack is 2cm wider than the acceptable limit, it is simply too wide.

Published Underseat Clearance by Aircraft and Cabin Class

Our findings indicate that very few airlines report under-seat sizes; therefore, it’s worth reading Delta’s aircraft pages to learn about their approximate under-seat dimensions. The numbers shown below have been provided by Delta, and were published as approximate by them on September 20, 2026.

There are two things you should pay attention to in that chart. First, there is the difference between an A350-900 and a 767-300ER. An A350-900’s maximum foldable width of usable space is approximately 15 inches, while a 767-300ER’s maximum foldable width of usable space is about 12 inches; therefore, a bag that has been size checked for an A350-900 cannot be guaranteed on a 767-300ER, despite both being long-haul flights operated by the same carrier with the same published personal item policy.

The second issue has to do with the sub-variants of a particular aircraft family. For example, although the 767-300ER and 767-400ER belong to the same aircraft family and have almost the same names when searching for tickets, they do not have the same under-seat measurements. Simply knowing that you are on “a 767” doesn’t give you the complete picture; you need to find out what sub-variant you will be using before making your reservation.

Cabin class changes the equation again and often does not fall within what one expects. Premium class cabins that feature fully lie-flat seats often do not have any traditional under-seat storage because of the position of the seat mechanism and the footwell. A person paying extra for a premium seat may find that they have less room to place their bag for take-off, landing or taxi; this is when the bag must be legally stowed.

How to Test a 20 L to 30 L Backpack Against Both Limits

It’s essential to understand that the measurements printed on bag labels are misleading at best and that this problem isn’t limited to smaller manufacturers, but affects many larger manufacturers as well.

Currently, Osprey lists their 20L Daylite Plus bag as having dimensions of 9.45 inches high x 11.02 inches wide x 18.9 inches deep – therefore, according to Osprey, a bag that is 18.9 inches deep and 9.45 inches high. No bag of this size on the market exists with this dimension. Similarly, other major retailers are using the same naming convention with one difference to lists bag dimensions; where Osprey lists the depth before the height, major retailers list the same bag’s dimensions are around 18 inches x 10 inches x 9 inches with a height of 18.9 inches. The three numbers all agree across all manufacturers. The difference is the way “height” and “depth” are arranged on Osprey’s specification sheet compared to the respective manufacturer’s specifications. When comparing “height to height” as stated on Osprey’s vs. an airline limit, you may actually end up comparing it to the wrong measurement completely.

To avoid this problem, do not be concerned with the naming conventions used. Just take your three measurements of your bag from longest to shortest; take the three measurements of your airline from longest to shortest. Compare them in the order you have sorted them. An airline’s under-seat opening doesn’t care how a manufacturer describes their height so neither should you.

Step 1: Measure the packed bag, not the empty one

Measure the bag after packing it up as it will be taken when traveling. Measure at the widest point of the bag, and ensure that the external pocket is stuffed to capacity and all compression straps are pulled to full tightness as they will be before boarding the plane. A 24 L bag that is empty versus one that is filled with a jacket is an entirely different thing. LATAM states that pockets, wheels, and handles will be included in the measurement of the bag, and therefore the bulges need to be measured and not the seams.

Step 2: Sort both sets of three numbers and compare in order

You need to now write down the three measurements from longest to shortest and then do the same for the published limit of each carrier. Then compare the longest measurement of each carrier with the longest, the middle with the middle, and the shortest with the shortest. To be accepted or cleared, all three must clear or pass. If any one measurement fails, the bag is a fail.

Step 3: Check the answer in both units

This is a required step because the measurement example of a 24 L Aer City Pack Pro 2 is published by the manufacturer as being 18 x 12 x 7 inches or 46 x 30.5 x 18 centimeters. Compared to American Airlines’ allowable personal item measurement of 18 x 14 x 8 inches, this pack will pass on all three axes with plenty of room to spare. The same allowed item measurement by American Airlines for the same pack using the metric conversion allows for a maximum length of 45 centimeters and its longest length is 46 centimeters, therefore the pack fails on that one axis.

The bag hasn’t been changed in size, and 18 inches converts to 45.72 cm with the US rounding down to 45 cm while Aer is rounding up to 46 cm. A decision is made by comparing the two rounded measurements. When you have a bag that’s already within 1 cm of either measurement limit, it is best to check both measurements and choose the stricter of the two when determining if your bag fits through the gate agent’s sizer and if the crew will consider the same measurement when making a determination.

Applied to the two packs above, against the limits verified on 20 September 2026:

A very popular 20 L daypack has been sold all over the world for travel, but it does not meet any of the 4 allowances, particularly on its longest side. This is indicative of the current state of the market and is why it is essential to verify underseat bag measurements before purchasing rather than at the gate. A personal item-size bag that is intended for genuine international travel should be designed to adhere to the dimensions provided by Lufthansa (40 x 30 x 15 cm) so that you have the maximum margin of error. Anything close to 45 cm on the longest side should be viewed as specific to that particular trip and not a generic size.

Seats That Remove Underseat Storage Altogether

Some passenger seat configurations are unable to accommodate personal items in the under-seat storage compartment. They are designed with no under-seat storage area, or due to FAA regulations on when you may stow your bag under your seat. Regardless of the reason, both have the same end result for a passenger with a compliant full-size backpack.

Bulkhead seats are the most evident example of this. There is no floor space available due to the absence of a seat in front, thus all luggage must be stowed in the overhead bin during taxi, take-off, and landing. Regarding exit row seats, there are even tighter regulations under 14 CFR 121.589, where carry-on luggage must not be stowed in a manner that would block access to an exit or impede the use of the aisle. This means that nothing can be located on the floor of an exit row seat during taxi, take-off, or landing, as cabin crew will enforce this rule consistently, and if a bag fits perfectly under that exit row seat, it is still prohibited from being stored in that location.

The third type of seat is the lie-flat business class and first class seats. The footwell, actuating mechanism and shell take up the floor space of this seat configuration and as a consequence, personal items can no longer be stored in under-seat storage. Delta Airlines has a clear policy stating that there is absolutely no under-seat storage available in some of their business class configurations.

None of these seats are negative selections; they simply shift the location for stowing your bag. If you anticipated that you would be able to keep your camera, laptop or medications under your seat from gate-to-gate, you should check the seat map for the airline before arriving at the terminal and boarding the plane.

Researching Your Own Aircraft and Seat Before You Fly

A couple of lookups will clear up the majority of travel situations before you even leave your home.

The first lookup is to find the specific aircraft associated with your reservation (NOT the route). This aircraft type will be on your ticket confirmation and/or in your airline’s manage booking section. You will take this information into each of the next steps in this guide. For the particular type of aircraft you are flying, you should also check your carrier’s aircraft page for that specific variant (this is where Delta has its underseat figures, and this is where the majority of other airlines have seat maps).

The practical tool for obtaining seat-level details has recently been modified. TripAdvisor’s SeatGuru was disabled in November 2025; its closest alternative, AeroLOPA, was developed by the same founder who built SeatGuru in 2001 and whose maps are to-scale drawings by an architect rather than sketches. The scaling of these drawings provides the critical component, allowing you to see where the legs of the seats and the boxes of equipment fit in the row you’re seated. This information would not be present on generic seat maps.

Most travellers overlook the fact that they have the ability to choose their own seat. While the space available under the seat varies from row to row, in the majority of instances it is the window and aisle seats that provide the greatest amount of space. In addition, the middle seat often has to accommodate the electronic box that is used for entertainment. If you are one of those travellers who needs to keep his or her bag under their feet for them to feel comfortable, then the seat you choose at the time of booking will provide you with a more significant benefit than any packing method.

Happy Day Turismo is a travel agency specializing in flight bookings, so we are able to offer you seat selection as a part of our booking process. Similarly, you can also make your own seat selection for free at the time you book your flight on your airline’s website. Both routes take you to the same plane and the seat maps are identical for both methods.

When a Compliant Backpack Still Will Not Go Under the Seat

When you find yourself in a position where you have followed the guidelines for acceptable piece size and measurement but your bag is still unable to fit in the overhead bin or under your seat, it is beneficial to be familiar with your options for Bag Recovery in order to avoid turning that unfortunate moment into an expensive mistake.

The primary reason people are unable to bring their carryon bags on American Airlines, particularly on American Eagle regional jets, has to do with the size of the plane in how it is designed or its shape. American Airlines has outlined this specific process in the carry-on baggage section of their website when choosing to fly American Eagle regional jets – any bag larger than the standard personal item dimensions is not allowed to be on board until you’ve checked it at the gate (valet-check it). Note that any bag that you check at the gate will be tagged and returned to you at the end of the jetbridge at your final destination. Keep in mind that the Embraer ERJ-175 regional jet does not have this policy of valet checking bags of this size as it can accommodate standard-sized carryon bags and there is no valet checking service available for this type of aircraft. This valet check is at no charge and was designed exactly for this purpose, however, it can only assist you if you check your bag before boarding; if your carryon is too large, you will not realize this until you reach the aisle of the aircraft.

The second reason for being unable to bring a bag on board is due to a full cabin. If an airline runs out of overhead space, the airline may place some cabin bags (like yours) in the aircraft’s hold. This is an operational matter for the airline and does not reflect negatively on you and your bag. If you are required to check your carryon bag, make sure you have available items you cannot be separated from i.e., medications, travel documents, valuables and power banks, in a small pouch that will allow you to remove these items in the brief time you will have available at the door of the aircraft.

Ultimately, the final say on whether or not your bag may remain on the floor by your feet lies with the aircraft crew’s instructions. If a crew member/in-flight staff indicates that a bag cannot stay under your feet, their instruction supersedes any airline’s minimum standards regarding carry-on bag limitations, regardless of what any airline’s page indicates. Disputing the measurement of a bag at the door of the aircraft only serves to unnecessarily delay the aircraft from taking off and does not impact the final decision about that bag.

Another related problem has a separate cause from the previous one, as well as a different solution than the previous one: A bag that fits within the published dimensions may still not fit in the metal sizer box at the gate because of the tolerances accepted in the manufacture of the metal size box. This “overhead bin” problem is very closely related to the previous bag problem, therefore, you should read the separate article by Bryan first before reading about the “overhead bin” issue.

O Que Levar à Mão no Embarque

A backpack must pass two different tests: the allowance set by the airline and the cavity provided by the aircraft. Passing one of these tests does not guarantee that a backpack will pass the other. To ensure that a backpack will meet your travel requirements, before making a purchase measure the widest points of the packed backpack and write these measurements down in order of longest to shortest. Compare these measurements against the size restrictions of the strictest carrier on your itinerary. If you need to use the backpack for travel internationally, also build to the size of Lufthansa’s 40 x 30 x 15 cm. Be sure to check any borderline measurements in inches as well as cm. By checking your measurements in this way you will know if the backpack can fit at your feet… and if you rely solely on a comparison chart’s numerical measurement you will find out at the boarding door what other options will cost you time or money.

Frequently asked questions

Can I put my personal item in the overhead bin instead?

In general, whenever there is excess capacity on a large aircraft, it is the decision of the flight crew to permit passengers to utilize that space for their carry-on bags or items. Generally speaking, airlines will designate the overhead compartment for full-sized carry-on baggage on all flights that are booked to capacity, and will dictate that passengers store their personal item(s) in the space beneath their seat(s).

Does a handbag count as a separate personal item?

On many airlines, a purse, laptop bag or small backpack is considered one (1) personal item, and is not in addition to the carry-on baggage allowance that has been published by that airline. If a passenger has both a purse and a backpack, it is common for them to be considered one (1) carry-on, due to the limitation imposed on combined size.

What happens if the cabin is full and my bag fits perfectly?

Airlines reserve the right to check cabin baggage into the aircraft’s hold as soon as the overhead compartment becomes full, and a compliant cabin bag does not provide an exemption. In the event that your medication, important documents, valuables or power banks are required during transit, we recommend placing them in a bag or container which is easy to access and which can be removed quickly. You are likely to receive very little notice prior to having to take such action.

Is a rolling underseat bag a better choice than a backpack?

It is highly unlikely that any of the airlines will permit the use of wheels or an adjustable handle for the sole purpose of transporting any item in a carry-on or personal bag. For example, LATAM Airlines has published weight limits on carry-ons, which includes the weight of the wheels and adjustable handle. In addition, both of these items add an inflexible depth that is greater than the amount that can fit into the space under a person’s seat or directly above the person’s head, where the majority of failures occur in the space underneath the seat.