(Yes, I’ve tried ALL of these packs! Reviews HERE!)
Like most things in life, there is no simple rule for deciding on a Camino backpack. It’s not just about how much gear you bring, but also the kind of gear. Small differences can add up to a large impact on what you’ll want your pack to be capable of (that’s why you might consider buying your backpack last). Below are some general guidelines that should help you think the decision through.

Measuring Backpack Volume

Backpack “size” usually refers to fit – not carrying capacity. So I’ll mostly be speaking in terms of “volume.” Many companies measure backpack volume by adding up the combined space of the closed compartments such as the main body or sleeping bag compartment or zippered pockets but not open “stuff ” or side pockets. Others measure every possible bit of storage capacity. So exact comparisons are difficult. To be sure, you really just need to try them out in person.

Visualizing Backpack Volume

Backpacks typically indicate their capacity in their names. If the pack’s name has a two-to-three digit number in it, it’s probably indicating liters. If it has a number in the four digit range, it’s likely cubic inches. Depending on your everyday experience, you’ll have a different frame of reference for what these volumes really indicate.

Here are a few rough comparisons between US standard and metric measurements that might help you think through your pack volume needs.

• 1/2 liter = large (“grande”) coffee cup
• 1 liter =  1/3 gallon, 1.3 quarts, or 1 large Smartwater bottle
• 2 liters = large soda bottle
• 3 liters = 1 gallon or 1 ream of standard paper
• 16.4 liters = 1,000 cubic inches
• 45 liters = 2,770 cubic inches or 1 airline carry-on bag (22″x14″x9″)

Choosing Backpack Volume

Numerous factors affect these guidelines, none should be considered universal!

Walking Packs

Packs in the 1-15L range are great if you just need to carry some some stuff while biking, jogging, or just a quick walk. At the low end you have belt or waist packs, at the higher end small hydration packs. Book bags usually fall into this range as well.

These are definitely too small for a Camino pack unless you are having your main baggage sent forward each day and only need a few daily supplies.

Day Packs

For 3-season hikes, day packs range from 15L-30L. (Mine is listed as 22L). This size range depends largely on activity and actual trip length. Going up to 35L lets you comfortably  carry more than one meal plus emergency extras (cf. 10 essentials). If you are hiking in winter (the 4th season), you will likely need more storage capacity (internal or external) for heavier/bulkier cold-weather gear and additional food/fuel.

If you are fairly minimalist, or have mostly lightweight gear, a pack in this size range will work for the Camino (I demonstrate a 22L, roughly 7lb. Camino load out HERE).

Overnight Packs

For 3-season overnight hikes, packs usually range from 30L-50L. (Mine is listed as 50L). Spending the night on trail adds substantially to the gear load as shelter and sleep systems become involved (see the Big 3) along with more food (and possibly a bear-safe container). Again, if you are hiking in winter, you will likely need more storage capacity.

This size seems to be the most popular on the Camino (see HERE). If you have “normal” clothing and gear (i.e., not ultralight), or have some specialized gear (like substantial photography equipment), this is likely the best range for you. (I show a 38L, roughly 17lb. Camino load out HERE).

Multi-Day Packs

Multi-day hikes are basically overnight hikes that last more than one overnight, and will likely get you into the 50L-100(+)L range with the low end reserved for ultralight hikers. If you are already geared up for an overnight hike, then food and water might be the only additions to your load out, so figure your daily volume needs for food and water and add that to your overnight pack. Winter considerations still apply here – especially since your food / fuel needs will be greater than on 3-season hikes.

Unless you are bringing some seriously heavy / non-compressible gear, there really should be no need to carry a pack of this size on the Camino. Although the Camino is in a sense a multi-day hike, it is more like a series of combination day/overnight hikes. You need more than a day pack for a minimal sleeping system and clothing, but you do not need shelter, fuel, or much in the way of food. Exceptions might include carrying gear for more than one person, or bringing a substantial amount of specialized equipment. In these cases, I recommend a lightweight, adjustable pack that can expand and contract as your needs change (EXAMPLES).

(Note that these considerations are unaffected by the so-called “10% Rule.” Your personal body weight has little to do with what you need or can carry.)

Testing Backpack Volume

A good idea is to do a test pack of your Camino gear without a backpack first. Organize it how you like, and then try to measure the total volume you need as well as the various pack volumes you’ll want for organization.

Keep in mind that 30L of total gear volume might not fit in a 30L pack because some of that pack’s capacity might come from small pockets that do not actually fit your packed gear (or, if the gear can be broken up into smaller “chunks,” it might mean poor organization). Therefore, a 40L pack might be better for 30L of gear depending on how that gear is packed.

Example

When I packed my gear into organized sacks, the total came to about 26L. So it seems I could have gotten away with a 30L pack.

However, when I organized the gear into stuff sacks and packed them into a 50L backpack, the main body filled up before I got to the 7L sack (which fit in the sleeping bag compartment). Without counting the external pockets (used for water bottles, snacks, sandals, and wet clothing) or the lid (which I removed), this “50L” backpack packed more like a 30L.

When it Comes to Size, Size is Not Everything!

Last, it is important to consider that backpacks are carry systems – not just bags with straps on them! The kinds of activities and loads a pack is designed for do not simply affect how big it is. Choices concerning the kinds of materials used, the type of suspension employed, organization offered, and other features are all impacted by not only how much is carried but what is expected to be carried (and where, and for how long).

These factors balance out differently for different purposes. An ultralight pack might sacrifice good back ventilation and cushioned straps for a low base weight, whereas a pack that only weighs an extra pound might be comfy and breezy. Then again, some ultralight packs are natively waterproof which is a rarity among traditional packs (which means you might need to pay and carry extra for a cover).

When we consider pack size/volume, a heavier pack may have a better suspension system that makes it more comfortable to carry heavier loads, but that does not function well with lighter loads. So while a small pack might not be a good choice for a multi-day hike, neither is a large pack necessarily very good for a day hike.

Example

In the above example, my gear came in at the low end of the Osprey Atmos 50’s  recommended carry weight. It might seem to make sense, then, to go with the smaller and lighter Osprey Stratos 36. However, as I explain HERE, the Stratos 36, though a good size for my gear, did not carry well for me. After 5 hours or so my lower back seriously ached. Although larger and heavier, the Atmos 50’s famous “Anti-Gravity” suspension almost makes the pack feel like it’s floating! For me, that’s worth the extra size (which is only about 8L with the lid removed) and weight (only 1lb. less than half the weight of  a full Smartwater bottle).

Conclusion

In the end, pick what is best for your comfort and health. Don’t let others dictate what you need – or don’t need – to carry. Make sure you are happy with the pack’s weight, comfort, and features. After all, no one else has to carry it!