How to Choose the Right-Sized Backpack

Before you head out on the trail, you'll need the perfect backpack. Read on to find out how to pick the right pack for your trip—and how to get the right size.

People with large backpacks hike along a dusty ridge

Photo by Eric Sanman

Your backpack is right up there in importance with your footwear—a poorly-fit pack can ruin your otherwise pleasant weekend trip faster than anything else. This is less of an issue when buying a 10L pack for day hikes, but infinitely more important when you need to carry more weight. Depending on your specific needs, there are a range of things to consider when buying a pack: capacity, fit, style, and features.

Capacity

Deciding which backpack capacity to go with is your first step in narrowing down your choices. This will usually be indicated in liters, with cubic inches often indicated in the product specifications. Depending on what you need the pack for, or how many days worth of camping gear and food you need to pack, your capacity needs will vary.

Day Hikes

For your average day hike, a 10 to 25L pack is the typical size. These are usually one chamber, with maybe a top/front pocket and a water bottle pocket. They’re meant for small items: snacks, a map, a small first-aid kit, water, or a light rain jacket. Some smaller packs will not come with a hydration sleeve, but most packs on the market today are designed as hydration packs.

Three backpack product photos side by side: a blue pack and two red packs

The Gregory Nano 14, Osprey Daylite, and Deuter Speed Lite 20 packs

Overnight / Weekend Trips

The next step up will be 30 to 50L packs, with a little extra space to hold gear for overnight hikes or weekends. Depending on your sleep system and if you have lightweight clothes, you can get away with a smaller pack. These are also great for day trips with extra gear, like camera equipment.

Three backpack product photos side by side: two grey packs and a black pack

The Mystery Ranch W Scree 32, Gregory Maya W 40, and Osprey Sirrus W 36 packs

Extended Trips

For trips longer than a few nights, you need a pack in the 50 to 70L range to be able to carry enough food for up to seven days. These larger backpacks are more capable of carrying heavy loads efficiently without impacting the wearer too much.

Three large backpack product photos side by side: a blue one, a pink one, and a grey one

The Deuter Aircontact Lite 45 + 10 SL, Osprey Aura AG 50 W, and Gregory Deva 70 W packs

Expedition Packs

The largest capacity backpacks are expedition packs, or anything above 80L. These are uniquely suited for winter expeditions and weeks-long trips where you can’t go light—Denali, Everest base camp, or backcountry trips with film, photography, or climbing gear. If you need one of these packs, you’ll know it!

A large green-grey expedition backpack

The Mystery Ranch Terraframe 80 pack

Fit

Like footwear, the fit of your pack matters, especially if you’re carrying any substantial weight. A proper fit will make the difference between an enjoyable or a miserable trip.

Getting fit in a specialist store is a great way to know your size, but you can do this at home! Your size is determined by torso length, NOT height.

The measurement you’re making will be from the top of your hips to the top of your spine, more specifically from your iliac crest to your C7 vertebra.

A photo of a man's back with diagrams showing the C7 and iliac crest

Photo by Taylor Nelson

If you’re measuring at home, you’ll just need a soft tape measure, or if you don’t have that, a string and yardstick will do.

Two side by side photos: a pink measuring tape and a ruler with string next to it

Photos by Taylor Nelson

First, find the two points you’ll be measuring from: your iliac crest and C7 vertebra. For the iliac crest, locate the top of your hip bone where your thumb can rest on the horizontal shelf, like in this photo.

A man demonstrates where to find the iliac crest

Iliac Crest. Photo by Taylor Nelson

You want the middle of the hip belt to sit right on your iliac crest.

Your C7 vertebra is the highest on your spine, located at the base of the neck. When you drop your head forward your C7 becomes visible, moreso on some of us than others.

A man demonstrates where to find the C7 vertebra

C7 Vertebra. Photo by Taylor Nelson

Now back to your waist—wrap the tape measure or string around your waist at the iliac crest and locate the point where the string meets your spine.

A man's back with a line drawn down his spine

Find the intersection of your waist line and spine. Photo by Taylor Nelson

From that point on your spine, measure directly up to your C7 vertebra.

A man holds a string against his spine

Photo by Taylor Nelson

That distance is your torso length!

A string is placed next to a ruler

This is my torso length. I’m 6’3”, and I’m barely a medium. Remember, height does not equal torso length! Photo by Taylor Nelson

There will also be a difference between a men’s and women’s fit. Women’s packs are designed for the female shape, so shoulders will be slimmer, and the hip wider in comparison to the shoulders. If you have a unique shape, consider trying on a men’s option.

The range for sizes goes:

Men’s

  • Small 16-19”
  • Medium 18-21”
  • Large 20-23”
  • XL 22-25”+

Women’s

  • XS 13-17”
  • Small 16-19”
  • Medium 18-21”
  • Large 20-22”+

Keep in mind that for the most part, the average male is a medium, and the average female is a small, with outliers being smaller. It’s very rare that someone is an outlier on the larger side.

Style and Features

Different Small Packs

Some small packs will be as minimal as can be—literally just a nylon container with shoulder straps. These are great for being ultralight and minimal and often won’t have a sleeve for a hydration bladder or a hip belt.

An orange lightweight pack

The Sea to Summit Ultra-Sil: the most minimal daypack on the market.

Others are more constructed and can hold a little more weight, as shown before. There are also hybrid packs that are both good hiking backpacks and good travel backpacks. These will be categorized by their features and construction. Typically, a commuter or travel pack will feature paneling and compartments that can hold computers or travel necessities.

Different Larger Packs

For any packs designed to hold more gear, you will usually see a frame construction, designed to bear heavy loads and distribute weight efficiently. Traditionally, packs designed for multi-day use were built with an external frame. They are not as common anymore, as materials have become lighter and more efficient, but they are occasionally still in use, especially with some hunting-specific packs.

A person in an external-frame backpack looks out at a sunrise

A traditional external frame backpack. Photo by Kun Fotografi

Internal frame backpacks are the standard on the market today. Unless you have very specific needs, an internal frame backpack is going to be your best choice. These still have a metal frame, but it is built into the structure of the pack and is much lighter. These packs hug closer to the wearer, providing better internal stability and ergonomics, efficient load distribution, and superior comfort.

The back of a backpack, showing padding

A modern internal frame backpack.

Lightweight Packs

Lightweight construction is also a big dividing line among mid-size and larger backpacks. While capacity can still be up to 80L, there are lightweight backpacks designed for carrying lighter loads. There are even frameless packs.

This requires a bigger up-front investment in a lightweight sleeping system, clothes, and cookware. Thru-hikers on the Appalachian Trail or Pacific Crest Trail prefer lighter packs and gear. However, these packs are specifically for lighter weight—you don’t want to carry more than 30lbs in them.

Features

The last thing to consider will be features. As mentioned, some minimal, smaller packs will not include a sleeve for a hydration bladder, but most packs on the market will be outfitted with a sleeve and some will even include a bladder. Other features include extra water bottle carriers, outer pockets for easy access, and comfort features.

Other important considerations are add-ons, like rain covers for adverse weather conditions. Gregory packs will come with a rain cover, while Osprey and Deuter covers are sold separately. Make sure to check the specifics.

The overall design of your pack matters too. Some are purely top-down construction, meaning everything has to be accessed from above. Other packs will have side zippers to access the interior without disturbing the top. Many packs will have a separate compartment for a sleeping bag. Most backpacking packs will have a removable top lid. There will be options with more or less outer pockets, straps, or attachments for small items or hiking poles.

All of these features will factor into your experience using the pack. If you plan to take longer trips and will be living out of the pack, some of the seemingly arbitrary features will play a much larger role in your decision making.

Conclusion

Your specific needs will determine exactly which pack you need, and know that you’ll likely end up owning different packs for different purposes. Don’t forget that fit matters more than anything! Utilize the help and advice of experts whenever you can, and know that packs are like anything else—if you buy a quality pack, it will serve you better and last you longer. Skimp on your tent, but not your backpack—your back, knees, and ankles will thank you later!

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Written By
Taylor Nelson
Taylor Nelson
Camping & Hiking Expert
As a History major, I have always been a consummate researcher and analyst. I apply these skills to my knowledge of the outdoor space. I applied and honed these skills while working at REI for 2 years, before moving into the brand side at La Sportiva NA. I worked in the field marketing department, r...
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