Best travel backpacks: how to choose one that fits your airline and your trip

A travel backpack has one job that a hiking pack does not: it has to be pleasant to live out of for a week or two, and then fit the rules of whichever airline you are flying. This guide does not rank products. It shows you how to choose a type of pack, what to read on a manufacturer's spec page, and which airline limits to check before you buy. For the wider range of bags and accessories, see the gear guides and the backpack section. Products are shown by type while partner links are set up, and price tiers are only a rough guide: $ is the lowest and $$$ the highest for that type, so read the live listing before you buy. How partner links work is on how we make money.

Most regret after a purchase comes from skipping one of four questions. Answer them in this order and the shortlist makes itself.

First, which allowance does your fare include? A pack that is perfect on a full-service airline can be refused at a budget gate. Second, how will you carry it? A ten-minute walk from the station is a different problem from an hour between ferries. Third, how do you like to pack? Some people want to open the bag like a suitcase, others are happy to dig from the top. Fourth, what is the weather like? A rolltop shrugs off rain, while a lightweight panel loader may need a rain cover.

Everything else, from color to the number of pockets, matters less. If you answer those four questions honestly, you will already avoid most of the common mistakes.

Airline limits differ by carrier and by fare, so check your own booking. The three examples below come from each airline's own help pages. They show why a single "carry-on size" does not exist.

Read the table as a set of questions, not a list of answers. Does your airline measure with or without handles? Does it set a weight limit for each bag or one total? Is the larger bag included in your fare or an add-on? Ryanair's general terms and its help pages describe the free bag with different dimensions, so rely on the page for your booking and confirm in the app. The same caution applies to any airline not listed here.

A clamshell pack unzips along three sides so the main compartment opens like a suitcase. For most trips of one to three weeks, with hotel moves every few nights, it is the type that causes the fewest problems. You can see everything, reach the bottom without unpacking the top, and keep packing cubes in neat rows.

Look for a boxy shape. A rigid back and firm side panels help the pack keep the same dimensions when it is full, which is what a sizer measures. Compression straps inside the main compartment stop the load from shifting. A laptop sleeve that opens from the back panel saves unpacking at security. A hipbelt that tucks away is useful on a long walk and easy to hide for a flight.

Watch for: front pockets that stretch. A pack can fit a sizer when the front pocket is flat and fail it when the pocket holds shoes. If your airline measures strictly, plan to keep the front pocket for flat items.

Skip it if: you need the free under-seat allowance only. Many clamshell packs are sized for an overhead bin, so check the dimensions on the manufacturer's page against the free bag size of your airline.

If your trip involves long days on foot, such as moving between hostels, trekking bases or ferry ports, a harness with a padded hipbelt moves weight from your shoulders to your hips. That is the whole point of the design. It also has trade-offs for travel.

These packs are often larger and deeper than cabin limits allow when full, and they weigh more empty. On a budget airline you will probably check one, or you will pack it short. If you do not plan to walk far with your bag, a clamshell is simpler. If you do, a hipbelt pack is worth the extra weight, and a zippered panel that covers the harness helps protect straps in a checked bag.

A rolltop closes by folding the top over and clipping it, usually in a coated fabric with welded or taped seams. That gives better weather protection than a zippered pack, and the pack shrinks to its load instead of holding air, which can help with cabin limits.

The cost is access. You pack and unpack from the top, so reaching the bottom means lifting everything out. The coated fabric can also feel warm against your back. A rolltop suits rainy-season travel, cycling to the station and trips where your gear will get wet. For a city break with a laptop and a lot of hotel changes, a clamshell is easier to live with.

A small pack sized for the free under-seat allowance is useful in two ways. It is enough for a long weekend if you pack with discipline, and it is a good second bag on a longer trip when you also carry a larger one. The limit on the free bag is exact on every airline, so measure the packed bag, not the empty one.

Expect less structure. These packs slump when half full and can be awkward to pack, so use cubes and keep heavy items against your back. A pack that looks right empty can bulge past the depth limit once you add a laptop and a jacket.

A plain panel loader, with a main compartment, a laptop sleeve and two side pockets, does the basics for much less than a feature-rich pack. If you travel a few times a year and pack light, you may not miss the extras. Be realistic about what you give up: thinner back padding, fewer compression options and, in many cases, little weather protection. Keep clothes in a bag inside if rain is likely, and check the packed dimensions the same way you would for a more expensive pack.

Product pages vary in quality, but the useful facts are on almost every one. Read these before you add anything to a basket:

• Dimensions in centimeters, not just liters. Liters describe volume, but airline limits are written as height, width and depth. If the page gives only liters, look for a spec table or a size guide.

• Empty weight. Compare it with your airline's weight limit, if there is one. A heavy pack leaves less for your things.

• Whether the front pocket expands. An expandable pocket helps you pack more and makes a sizer harder to pass.

• Harness design. Padded, shaped shoulder straps and a sternum strap matter more than the number of pockets. Check whether a hipbelt is removable.

• Opening style. Clamshell, top-loading and rolltop each suit a different packing style.

• Water resistance. A coated fabric helps in rain, but taped seams matter too. A water-resistant claim is not the same as waterproof.

• Laptop sleeve size. Check the sleeve against your laptop's dimensions, not just its screen size.

• Zips and warranty. Chunkier zips and a clear warranty tell you something about the maker's confidence.

When two products look the same on paper, the return policy is a tiebreaker. Buy from a seller that lets you pack the bag at home and measure it against your airline's limit.

Whatever you buy, test it at home before you travel. Pack the bag with the clothes and gadgets you plan to take, close every zip and measure it with a tape measure, including handles and straps. Weigh it on a luggage scale or a bathroom scale. If your airline lists a weight limit, remember the pack is part of the total.

These habits make a pack easier to fit through a sizer:

• Pack heavy and bulky items in the main compartment, close to your back.

• Keep front pockets for flat items such as chargers, a passport wallet and a pair of socks.

• Use packing cubes and squeeze them so the load stays square.

• Wear your bulkiest layers instead of packing them, but check whether your airline weighs only the bag or also what you carry.

• Tighten every strap, including side compression straps, before you reach the gate.

The most common mistake is buying on liters alone. Two packs of the same volume can differ a lot in depth, and depth is what usually fails a sizer. The second is buying for the bag you imagine, not the one you will pack. If you always bring a laptop, a rain jacket and a second pair of shoes, buy for that load.

Other mistakes are quieter. People pay for a hipbelt they never use. They buy a rolltop for a laptop trip. They choose a pack that is comfortable empty and punishing at the weight they actually carry. And they forget that fares change: a pack that fits your usual airline's free bag may be wrong for the carrier you book next month. For airline-specific advice, see carry-on packs for budget airline sizers.

If you travel with a suitcase, take taxis from the station and rarely walk more than a few minutes with your bag, a travel backpack will not improve your trip. A good wheeled carry-on is easier on your back on smooth floors, and in cities with lifts and escalators at most stations it works well.

You also do not need a new pack if you already own one that is comfortable, fits your airline's limits when packed and opens in a way you can live with. Measure it packed, weigh it and take it on a short trip before you replace it. A tape measure and a kitchen scale at home will tell you more than any product description.

If your trip includes long train days and you need power for a phone or laptop, see travel routers and power banks. For a packing list built around a single cabin bag, start with what to pack for Japan in spring.