An Essential Guide to Backpack Sizes and Volumes

Backpack sizes are confusing. I get it. There seems to be an endless array of options and volumes (measured in liters, no less). Plus, backpacks come with so many different styles, attachments, zippers and damn pockets just don’t always make sense.

What is the difference between backpack sizes? Which one is best for me? Is there a difference between travel backpacks and the ones I might take on a weekend camping trip?

Whether you are planning your first backpacking trip or replacing luggage for a more convenient travel backpack, understanding different backpack sizes and volumes can seem daunting at first.

But it doesn’t have to be.

If you’re like me, you may feel intimidated by the ideas of taking your questions about backpack sizes to the sales rep at your local outdoor outfitter. Maybe you want to avoid their quiet judgment while you ask what the difference is between a 20L daypack and a 50L backpack. Or, maybe, you just prefer to do the research on your own and come prepared, ready to buy the perfect backpack size for you.

Either way, I tried to cover all the basic essentials of backpack sizes and volumes in this post – so you will know exactly what to look for before embarking on your next epic adventure.

You may also be asking yourself, “Well I want to know about backpack size, but don’t I also need to know about fitting a backpacking pack for my body?” That’s a great question, and we will get to that – but not quite yet. Whether you are going on a backpacking trip to a nearby park or about to do some around the world travel, there are a number of important differences in regards to capacity and fit. And knowing what is right for you in both departments can make or break your entire adventure! However, this post will focus solely on volume and capacity for now.

Okay, enough small talk. Past the appetizer and onto the main course.

It’s time to learn how to decipher backpack sizes and find the perfect one for you.

It’s good to start by knowing the length of your trip and the items you wish to carry (or, perhaps more importantly, how much weight you are willing to lug around on your back during an extended trip). Remember: bigger is NOT always better when you have to carry it up mountains and across international airports!

How Do you Measure Backpack Sizes?

Unlike regular luggage, camping and travel backpacks are measured by their carrying capacity, not dimensions.

This is because backpacking packs may not have set rectangular shapes (they are usually curved to conform to your body and be more comfortable) and it allows people to understand how much their pack can hold when planning an extended trip or around the world travel.

Now, to make matters more confusing, different backpack companies can use different units of measurement when describing capacity and volume. They will all generally express the volume of their packs in liters or cubic inches. Some companies will be nicer than others and just do both on sizing charts for more universal consumer convenience.

Training your brain to think of backpack sizes in liters will be helpful. This sizing metric tends to be a bit more mainstream and can often make choosing the right pack easier overall.

Any backpacks that have a number correlated with their name are telling you their size outright. For example, the backpack that I lived out of for six months in Puerto Rico and Central America is very similar to the “Osprey Aura 50L.” What Osprey is telling you with this name is that this pack has the capacity of 50 liters.

Since backpack companies like to have well-rounded numbers, the liter amount may not be exact because they will round to the nearest whole number. Still, it gives you a good baseline for the backpack’s size and the amount it can hold – just by reading the name.

Most people have trouble visualizing how much that 50-liter pack can actually hold. I know I did.

The most common visualization given (and I think, the easiest) is to use your Nalgene water bottle as a backpack size guide. Hear me out. The standard Nalgene is a one-liter bottle. So, the liter size of a backpack would be equal to how many Nalgenes full of water you could dump into the pack. In my example above, I could theoretically dump 50 Nalgenes in my travel backpack. 

Not a perfect comparison when completing your camping gear list, but a good starting point.

If the backpack size is measured in cubic inches, the exact volume will be what is advertised, as they will often include decimal points instead of rounding. It has also become more popular for backpack providers to give conversion charts from liters to cubic inches and vice versa.

If you are calculating backpack sizes on your own, it’s good to know that 61 cubic inches = 1 liter.

Finally, you may have also noticed that some brands will have different packs for men and women. This is to make it a better fit body shape and hip sizes for a more comfortable fit while hiking. Everyone’s body is a little different and sizes vary from brand to brand. Don’t be turned away just by the gender correlation to the pack. I have a number of guy friends that ended up choosing a women’s pack because it fits them the way they wanted.

It all comes down to what sits right on your body.

I always like to go into a store and let the salesperson be my backpack size guide. They’ll measure you, help you buckle up and even give you some weighted bean bags to put in your pack and make sure it’s still comfortable after a few minutes.

It’s also important to note that, fit and capacity are not always correlated. It’s possible to buy a large capacity backpack size even if you are petite and need a small frame backpack.

How to Choose Your Perfect Backpack Size

Now that you have a better handle on the numbers, it is time to go back to that original question of knowing what you are going to be using your backpack for. If you have yet to go on your first backpacking trip, you may not know where your adventures will take you yet.

Here are a few things to consider…

Are you going to strictly be doing day hikes? Are you planning a thru-hike? Will you be using it for weekend backpacking trips? Are you looking for the best travel backpack that will allow you to carry everything you need around Europe for a summer?

Here’s a quick backpack size guide with the most common capacity ranges (in liters) as they correlate to the standard adventure uses:

The Essentialist (Daypack) → 0-10 liters

When you are carrying a pack that is less than 10 liters, you are going to be packing light. This could be as simple as a hydration-style pack you take on trail runs or a small daypack backpack that’s comfy to you.

A backpack size this small will merely cover the essentials. Think water, a snack or two, a light jacket, and a few first aid supplies for emergencies.

The Transient Traveler (Overnight Trips or Extended Day Hikes) → 10-30 liters

If you are planning a day hike that truly takes all day or the hike includes other activities, like rock climbing or canyoneering, you may need something a bit larger to fit the extra food, water, clothing layers, first aid supplies, and gear.

A 30-liter pack can also be something you use for a quick overnight out and back trip in warm, dry weather.

Expedition Edition (Ultra-Light Thru-Hike, Weekend Trip, or International Travel) → 30-50 liters

Perhaps you have an extended camping trip on the horizon. Maybe you need to upgrade your travel backpack for those upcoming international trips. A 30L – 50L backpack will be just the ticket. It will be able to hold all your sleeping, cooking, and camping gear you need for trips up to 5 or 6 days.

As thru-hiking has evolved, many hikers have taken on a truly minimalist philosophy (this applies to their backpack sizes). Packing light allows them to cover more miles at a faster pace, restocking when needed. As for international travel, this backpack size range is perfect for a number of reasons – but I’ll get to those later.

Going Off The Grid (Multi-Day Backpacking) → 50-70 liters 

Sometimes we just need a break from it all. Say… a 10-day break out in the woods or mountains where the only contact to society is the friends you’re with. Or, if you’re alone, the occasional airplane overhead.

This will require a larger capacity pack for a few reasons.

For starters, you’ll simply need more room to carry food and water (if there is no water source to filter from). And if you want a camping vacation-style trip, you may want a few luxury items (i.e. books, nicer cook gear, pillow) in addition to your clothes, first aid kit, and standard camping gear.

Pathfinder (Winter Multi-Day Trip or Hiking Guide) → 70+ liters

A pack larger than 70 liters seems a bit ridiculous (and impossible to carry) at first. But, depending on your situation, it might be necessary.

Do you want to pack out in colder conditions or head up the mountains? You will need to have cold weather camping equipment and clothing. All of that is a lot bulkier and harder to fit so you will simply need a larger backpack size.

You may also be traveling with others who rely on you (like kids) or starting out as a backpacking guide. If that’s the case, you will not only have to carry your own equipment, but you will need to carry extra safety equipment for those with you as well.

Ultimately, size comes down to knowing what you want to do and how much you want to carry.

It goes without saying, everything you are taking with you will literally be on your back. Think about if you want to carry all of that stuff up a mountain. Or if it will fit in the overhead bin as a carry on for international flights (most sizes over 50L won’t).

Little things add up in weight. So, really think about what you need, not just what you think you might want.

This might mean you practice packing a few times before you leave for your first backpacking trip with new gear. You may also want to test your backpack size. Do this by packing it and walking up and down your stairs a few times. If you’re anything like me, it might take a trip or two before you have found the perfect life-sustaining system you can happily carry for miles at a time.

Just be patient with yourself. A backpack is a big purchase. But finding the right one will give you a leg up when it comes to completing your camping gear list.

What is the Best Size for a Travel Backpack?

Backpacks aren’t reserved for outdoor adventures!

A lot of people ditch a suitcase for long term travel. Especially when staying in a hostel or moving from country to country a lot. I personally only use a backpack when doing an international trip. My best advice in this situation is to get something that can be considered a carry on bag. This will ensure that your belongings stay with you and you can avoid the check baggage fees.

Most airlines allow carry-on luggage up to 22″ x 14″ x 9″. You may also see a limit of 45 linear inches (length + width + height).

Now we have to use those backpack size conversions I mentioned above.

A pack measuring 22″ x 14″ x 9″ is 2,772 cubic inches in volume. Just multiply the three measurements together. 2,772 cubic inches translates to 45.2 liters. A 45-liter pack will afford you all the space you will need for international travels with none of the hassles of checked luggage.

Just be sure to check before you purchase a plane ticket! All airline rules are a smidge different, especially budget airlines (lookin’ at you Spirit and Ryanair, fans). 

What’s Next?

Backpack sizes shouldn’t intimidate you anymore!

So maybe you’ve decided the right capacity or volume your pack needs to be. Let’s not forget how it should fit.

Nothing makes a great adventure go south like an incessant pinch between your shoulder blades. Having a pack that fits well is important. It will be one of the best time investments you make when it comes to planning your adventure travels.

I believe that pairing the right sizing in liters with the perfect backpack fit is something you can do yourself!

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