How to Choose the Right Backpack Size for One-Bag Travel

Choosing the Right Backpack Size for One-Bag, Minimalist and Ultralight Travel

If you're new to one-bag travel, you may find yourself wondering, what size backpack should I get?  Well, I'm here to break down the various options and considerations that are worth taking into account, and hopefully point you toward a solution that works best for you.

 A quick note on sizing:

I see a lot of people ask.. How do I pack for three weeks in Italy, or two months in Norway, or six weeks in Southeast Asia, etc. - which is fine, as they all have variable climates, but the interesting thing to note is that the length of the trip doesn’t matter.

One-baggers who have been doing this for long enough understand that the length of a trip doesn’t matter; a week, a month, or a year, we pack the same size bag, and usually, the same stuff (give or take a few clothes, depending on climates).

As a long-time one-bagger, I can tell you I pack the same 1x pair of pants, 2x shorts, 4x shirts, 7x underwear, and 7x socks for every trip, hot or cold, of any length. The only difference is that I add 3x crew socks, 1x puffer jacket, 1x outer waterproof shell layer (top and bottom), and thicker boots for winter travel.

I still use the same bag, it's just packed to the brim for winter travel, versus lighter and smaller for summer travel.

I'll touch on this later, but with this concept in mind, let's talk about capacity.

Backpack Size and Capacity

Travel backpacks come in various sizes, typically measured in liters. The most common sizes for one-bag travelers fall in the 30-40L range, ideal for carry-on luggage. However, if your trip involves heavier clothing or specialized equipment, you might need a larger pack (more on that later).

Here’s a quick overview of typical sizes and use cases.

• <30L: Suitable for weekend trips and minimalist, ultralight travel, can fit under most airline seats, and can double as a hiking backpack.
• 30-40L: The most common sizes for one-bag travelers, ideal for carry-on luggage, might fit under airline seats, *may work for hiking
• 40-50L: Good for extended trips that require additional winter gear or specialized equipment.
• >50L: This is what we call "overpacking"

When it comes to one-bag travel, it's important to consider airline limitations, and unfortunately, those limitations vary widely, so we've broken down the important metrics into two charts, under-the-seat (personal item) size regulations, and carry-on size regulations, for some of the more popular domestic and international airlines. 

Personal Item Size Limitations

Carry-On Size Limitations

These tables aren't all-inclusive but should give you an idea of what size ranges to look at. You can see that carry-ons are generally in the 30-50L range, while personal items are about half the size, somewhere in the 10-30L range. Anything over 50L has a high risk of needing to be checked.

It's important to note here that many one-baggers (myself included) are actually two-baggers, or perhaps more accurately, we have one primary backpack and a second, smaller day bag/personal item; so let's discuss the pros and cons.

Packable Day Packs

Packable day packs effectively add ~10-30L carrying capacity and take up almost no bag space, a good example is the Sea-to-Summit Nano Sil Day Pack (20L), but there are a bunch of budget options (including some on our site).

I've argued in other articles that a day pack is a one-bagger essential, with uses ranging from dirty laundry, to beach trips, to day hikes and more; but I don't want to get too far off course.

The point is that you may not need a 50L bag, you may need a 40L bag with a 20L add-on, or a 30L bag with a 15L add-on, etc.

The only downside to these ultraportable day bags is that they aren't built for long-term comfort; they don't have frames, sternum straps, load lifters, or shoulder pads, so consider your use cases before selecting a day pack.

Detachable Day Packs

• Osprey Farpoint/Fairview: Feature a removable 13L daypack

• Deuter AViANT Access Pro: Comes with a detachable 10L daypack.

When deciding on your backpack size, consider opting for a primary backpack and a secondary day pack; you'll keep all the benefits of one-bag travel, with the added benefit of a short-term hiking/day bag and extra capacity.

It's worth noting here that anything under 30L should be fine for doubling as a hiking backpack; meaning if you can fit everything you need in a 30L backpack, then you likely don't need a day pack, your same backpack can be used for day trips, short hikes, gym runs, grocery store runs, beach days, park hangs, etc. 

It's fairly common in the one-bag community to use the same bag for everything, it's one of the benefits of one-bag travel - fewer things to manage!

Expandable Capacity

Some backpacks feature expandable zippered sections, allowing you to increase capacity when needed. Notable examples include:

• Peak Design Travel Backpack 45L: Expands from 35L to 45L.
• Timbuk2 Never Check Backpack: Expands from 40L to 50L.

As a personal preference, I opt for detachable day packs over expanding storage, since they serve multiple use cases and give you added capacity, but if you prefer an all-in-one bag, both of these options are good.

External Attachments

Loops, hooks, and straps allow for attaching additional gear to the outside of the pack; common use cases include shoes, wet towels, dirty clothes, water bottles, etc. I won't dwell on this too much, but it's worth noting if you're at the threshold of 30L to 40L or 40L to 50L - you may be able to size down.

Compression Straps

Something to look for as you're conducting research, internal and external compression straps, they both perform a similar function, internal straps are good for compressing your contents while packing, and external straps offer a second level of compression once you have everything packed; both are useful and great to have in any travel backpack.

Note that if you’re using vacuum seal bags (which you should), then internal compression straps aren’t as important; they're still nice to have, but you should be vacuum-sealing most of your items before packing even begins.

Sizing Your Backpack for Body Type

This is all good info, but how do you know what size fits your body?

At this point, there’s a limit to how much we can help; one of the most difficult things to get right when it comes to sizing is how the bag fits - not just your stuff, but also YOU.. especially if you’re browsing online.

We don't know your measurements, and there’s no way for us to show size charts for every backpack on the market, but here’s a quick example of various size backpacks for men and women.

To get the fit right, we highly recommend going to your local outdoor outfitter and trying out a few packs; you don’t have to buy from them, but they should help you understand both backpack sizes (how much the backpack fits) and backpack sizing (how the backpack fits you).

We cover body sizing extensively in our post How to Choose the Perfect Backpack for One-Bag Travel, which is a deep-dive on all the factors to consider before choosing a backpack.

Quick Detour

Up until this point, we've assumed you have your packing list largely hammered out, but an article about bag size wouldn't be complete without a reference to minimizing your pack. If you haven't already, check out a few of these useful tips for minimizing what you bring.

• Top 10 Tips for Minimizing Your Pack
• 8 Tips for Packing Fewer Clothes
• The 14 Most Over-Packed Items for Long-Term Travel
• 6 Simple Packing Rules for Minimizing Your Pack

Popular Travel Backpacks

So you have a size in mind and you have an idea of what fits, now it's time to choose a backpack (or two).

We recently covered the best travel backpacks in our post, Top Travel Backpacks for One-Bag Travel 2024, but if you're still not sure what to look for in a travel backpack, check out How to Choose the Perfect Backpack for One-Bag Travel - where we go into extensive detail on all the things worth considering when it comes to buying a backpack.

Testing

The last step in choosing the right backpack size is to simply TEST them, in the flesh, with your stuff. There's no easy way around this, especially since you likely won't have access to every backpack on your list. But you must test your pack before committing.

This thing may be your sole companion for the next few weeks, months, or even (hopefully) years, so make sure it's comfortable, it fits your stuff and you like putting it on. Like shoes and travel clothes, getting this right before your trip is incredibly important, so don't be shy about trying a few of your top contenders!

Conclusion

Choosing the right backpack size comes down to two things, the right size capacity and the right size fit for your body type; it's important to get both of these things right before investing in a long-term travel bag.

The best approach to getting sizing right is to:

1. Decide on the one-bag or two-bag approach,
2. Make your best guess in terms of capacity,
3. Go to your local outfitter and get a feel for what works (for both capacity and body size), and
4. Test your options - purchase one or two of your top contenders and make a final decision once you've felt and packed them.

Thanks for reading, and as always, happy travels!

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