One of the most important things to consider when packing for a trip is what size backpack you will need. Depending on the length of your trip and what you plan on bringing with you, you'll need to choose a backpack that's big enough to fit everything but not so large that it becomes cumbersome to carry.

Luckily, there are a few guidelines you can follow on how to choose the right backpack size for your needs.

Here's a quick cheat sheet to get you started:

Most backpacks are measured in liters (or "litres" if you're shopping in the U.K., Canada, or Australia)! This is the capacity of the backpack, or how much it can hold.

How To Size a Backpack and Choose the Right Fit

Consider the following factors when determining what size backpack you'll need:

Torso Length

The right backpack fit depends more so on your torso length than your height. Try measuring the distance from your iliac crest (the top of your hip bones) to your C7 vertebrae (the knobby bone at the base of your neck), or ask someone to do it for you. Then, consult a sizing chart or look for the size on the product page when shopping online. If you're not sure what your torso length is, most retailers will have staff who can help you find the right size. If the backpack sits too low after adjusting the straps, it's too big.

Frame or Backplate

Some backpacks come with a curved backplate that can help distribute the weight of the bag more evenly and make it more comfortable to carry. It can also keep your bag upright when you place it on the ground. Others are frameless or have a slightly padded back, which is what most school backpacks have. Depending on your trip, you may prefer one style over the other. If you're planning an expedition, it's always a good idea to inspect the frame, as a sturdy one can make all the difference in comfort.

Pockets and Compartments

When figuring out what size backpack to choose, consider the amount of storage you'll need. If you're planning on carrying a lot of gear, look for a travel backpack with lots of pockets that can help you keep everything organized. On the other hand, if you're just bringing along a few essentials, a smaller bag with just one or two compartments might be all you need. This could be a daypack with less capacity or a sling belt that doubles as a crossbody bag.

Small Backpacks: 10 to 24 Liters

Suitable for: Commuting, quick shopping trips, an evening jaunt, or other short excursions where you don't need to bring much with you.

Not suitable for: Day hikes, expeditions, or multi-day backpacking trips.

Knowing what size backpack to choose is essential for any trip, whether it's a quick jaunt around town or an extended backpacking adventure. Small backpacks usually have a capacity of 10 to 24 liters, which is just enough space for the essentials. If you're only planning on being gone for a few hours, this is the ideal size. But if you're packing for a longer trip or need to bring along more gear, you'll need a bigger backpack.

Medium Backpacks: 25 to 40 Liters

Suitable for: Gym trips, day hikes, international travel (as a personal item), overnight or weekend trips (when packing light), or any other situation where you need to carry more than what a small backpack can hold but don't want the bulk of a large pack.

Not suitable for: Extended backpacking trips (usually more than 3 days) where you need to bring a lot of gear.

Figuring out what size backpack to choose boils down to what you'll be using it for. If you need a bit more space than what a small backpack offers but don't want to lug around a large pack, go for a medium size. These have a capacity of 25 to 40 liters, which is just enough room for a change of clothes, a laptop, and these must-have travel accessories for every destination.

Large Backpacks: 40+ Liters

Suitable for: Extended backpacking adventures, long-term camping, expeditions, international travel, or any other situation where you need to carry a lot of gear.

Not suitable for: Short hikes, commuting, or other short excursions where you don't need to bring much with you.

When it comes to what size backpack to choose, bigger is usually better for extended trips. Large backpacks have a capacity of 40 liters or more, which is plenty of space for all your travel gear, even on longer journeys. If you're planning a backpacking trip for seven to ten days (or longer if you're travel-savvy and can pack light), this is the size you'll want.

Now that you know what size backpack to get, it's time to start packing for your next adventure!

Happy travels!