How Big Is a 40 Liter Hiking Backpack?

By Thomas Sorheim •  Updated: 05/06/20 •  5 min read

If it’s your first time shopping for a hiking backpack, it can be a little bit difficult figuring out which bag is right for you. How are you supposed to know what size to go with? What’s the difference between a 30L bag and a 40L bag?

Relax and take a deep breath. We’re here to help you sort it all out. While there’s a wide range of available hiking backpack sizes and volumes, for most people, a bag with a volume between 30L and 40L will be more than adequate for the majority of your hiking needs.

We personally prefer to use 40L hiking backpacks, for reasons which we will be explaining in this post. Keep reading to find out why it might also be the ideal size for you as well.

General Backpack Size Info

There’s typically two types of measurements used when measuring the size of a backpack – the actual height/length/width measurements and the volume, or total carrying capacity. You can generally get a rough estimate of a bags volume by calculating its dimensions, but that method is far from 100% accurate.

As we’ve mentioned before, there’s three main things to consider as far as size goes when purchasing a hiking backpack:

Three persons are standing with the backpacks and looking over to the mountain

So How Big Is a 40L Backpack?

To give you an exact idea of how big a 40L backpack is, first you must understand how that measurement is determined.

Typically, a backpack manufacturer will measure the volume of all of the available compartments on the bag and then combine them all together to get the total volume result. They will measure the main compartment, along with any other pockets that can be opened and closed.

These measurements are taken in cubic inches and then converted into liters. It should be noted that the measurement is usually rounded to the nearest decimal points, meaning that they aren’t always 100% accurate.For reference purposes, 40L is equal to 2,440.95 cubic inches.

So that’s the exact answer for how big a 40L backpack is. With that out of the way, let’s go over some of the reasons why 40L is the ideal sized bag for most people.

A woman going over the bridge with the backpack

Why 40L Is the Ideal Size Backpack?

The most commonly recommended size for hiking backpacks falls between 30L and 55L. We find that 30L is simply too small to pack the items you’ll need for any hiking trips that will take more than a few hours.

On the other hand, while 55L will let you pack everything you’ll need with ease, it can be rather bulky to carry. It’s also important to note, especially if you plan on any airline travel with your backpack, that within that range, most airlines require you to check in most bags over 45L.

So, with that in mind, we think that 40L is the best volume to go with. It manages to strike a perfect balance. It’s not too bulky as to require being checked-in (no risk of losing your checked luggage and saving you precious time in airports), yet it’s still large enough to be able to hold all of your things.

A backpack with a 40L volume is the perfect size for both short and sweet hiking trips that only take up an afternoon of your time, and for traveling adventures that can last anywhere from six months to a year. It’s important to note that just because we recommend a 40L backpack, that doesn’t mean you can’t go with a smaller or larger size if you’d prefer.

If you have a lot of stuff to pack and you won’t be going through any airports anytime soon, don’t hesitate to go with a 55L bag. On the other hand, we know of many people who have been traveling for over two years straight with only a single 30L backpack.


A 40L hiking or traveling backpack is the size that we most often recommend for anyone purchasing their first bag. It’s the perfect size for most beginners, striking a balance between having plenty of capacity available, while also being comfortable to carry. It’s also an ideal size if you plan on traveling extensively, as you won’t have to check your bag and can take it as carry on instead.

However, as we mentioned, that’s only a general recommendation. As noted above, you are usually pretty safe to go with any backpack size that falls somewhere between 35L and 55L. If you are ever in doubt, remember to keep in mind the three important sizing considerations as well: your size, your excursion plans, and how much you plan on packing.

By keeping all of these factors in mind, you will be able to find the backpack that’s just right for all of your needs.

Here are the best 40L backpacks:

Deuter Futura PRO 40 Hiking Backpack

Featherlight, durable, and brilliantly versatile, the Futura Pro 40 is a top-loading, all-season pack designed for advanced-level hiking and urban excursions, no matter the weather.

Lightweight construction totals 3 lbs 9 oz. with packable volume of 40 liters

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Gregory Mountain Products Zulu 40 Hiking Backpack

Free float suspension: low profile open air ventilation, moisture wicking mesh and custom torso length.

3D comfort cradle system: an ultra comfortable, body hugging fit.

Front stretch mesh pocket: for easy access while on the trail. Volume: 40 liters.

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Thomas Sorheim