A hike becomes a backpacking trip when you carry all the equipment necessary to stay out overnight, consisting of shelter, sleeping system, and cooking equipment, food and water. For one night or a dozen, the basic kit is the same, with adjustments for food and fuel. How you carry it will determine the enjoyment level of the trip. If the weather and terrain are not comfortable, that's part of the experience. If your pack isn't, you might not go backpacking again.
To carry a load comfortably, remember the the old saw to 'lift with your legs, not your back.' Until the 1950's, a backpack was just a bag that hung from the shoulders and relied on the back muscles to carry the load. Wooden frames were used in some designs to provide structure, but still had only shoulder straps. The development of the lightweight tubular aluminum frame and padded hipbelt that moved the weight to the leg muscles was the innovation that allowed backpacking to become a viable activity. As technology improved and people went farther and longer into the backcountry, the classic external frame pack design has been largely replaced by the internal frame, where the suspension is tied directly to the pack bag, creating a closer, more tailored fit.
The weight and construction of the whole pack will be oriented toward a specific size of person as well as the size and weight of the load. Lighter overall pack weight anticipates less and lighter gear and careful handling. A heavy pack has been designed for any and all loads and treatment. If you are honest with yourself about how much stuff you bring with you into the backcountry, you'll be more successful with your pack selection. Another factor is the brand's focus. For example, Osprey and Deuter are companies that primarily make packs. Many larger outdoor brands make such a wide range of products, they might not be as successful in such a specialized category.
Most active backpackers will admit that over the years they have built a collection of gear that is about five times the amount they need for any one trip, because no two days on the trail are the same, and the right kit for April in Western New York is very different for the same weekend in Big Bend National Park. With that in mind, it is possible to buy a pack that will work for most of your trips, understanding that sometimes it will be a bit big, others a bit small.
When talking about backpacks for the trail, they will be described by two sizes; the torso length and volume. The volume or cargo size will tell you how much you can carry. Torso size will determine if it fits you specifically and comfortably.
As a reference, most school bookbags have a cargo capacity or volume from 1800 to 2200 cubic inches, or 30 to 41 liters. You will see both measurement systems, and the conversion is that a liter is roughly 60 cubic inches. As you shop, note that pack model names will frequently indicate the volume, such as the 'Tankard 3200' (cubic inches) or 'Scabbard 43' (liters). With some quick mental math you can compare bags of similar capacity.
For this discussion, anything under 40 liters will be considered a 'day' pack, because you only have enough room for supplies for a day. 40-50 liters is a 'day and a half' pack because you have just enough room for basic shelter and sleeping system and not much else. Most packs in the 50-70 liter range will work for two to seven nights and are the most popular. Packs above 70 liters are large and heavy and are really only useful for 'big' trips with heavy equipment requirements and/or little support or infrequent resupply.
Be honest with yourself - how many nights are you really going to spend out, and in what kind of conditions? How often will this pack be used? Are you willing to tailor your gear to the trip, or are you bringing the same kit each time? Big bags encourage overpacking, but undersizing might mean replacing or omitting gear. How much money do you want to spend? Cheap or missing equipment can ruin a trip, so make sure to keep all this in mind. Also, internal frame packs rarely have much internal organization, as the extra fabric and stitching adds weight and complexity. As a result, expect to build a collection of cloth stuff sacks for organization.
Empty pack weight should hover around 5lbs/2.25kg. Dropping below 4lbs means the bag won't carry much weight and durability has been sacrificed to reduce weight, and while packs over 6lbs will be more substantial and feature beefier suspensions, you're paying a weight penalty before you put anything in it.
Standard design and features will include a top-loading cylindrical shape with one or two drawcords, internal hydration 'slab' style pocket and port(s) for the drinking tube, pocket lid with quick-release and adjustable straps, removable cargo divider about two-thirds of the way from the top, panel access to the bottom of the bag, and external pockets and/or panels for water bottles and quick-access storage. Panel access for the main compartment is becoming more common, as are included accessories like raincovers and lids with a fanny pack option.
The hands-on selection process begins by knowing your waist and torso measurements. You might already have an idea that you are long or short torso, and what your waist measurement is based on your clothing, but pack designers are not subject to the whims of fashion, so you should measure and find the actual numbers to use when choosing and fitting a pack.
The fitting process is best achieved with measuring tools at your local outdoor shop, but you can get close at home, with some assistance.
- Wearing a T-shirt and elastic waist shorts or pants, grab a tailor's measuring tape if you have one, but otherwise a regular flexible measuring tape will do.
- Adjust your waistband so it is right at the iliac crests, the forward points of your pelvis. They are pretty easy to find with your thumbs, about where the pockets on your jeans sit. Make sure that the waistband is level all the way around, and take your waist measurement there.
- Face away from your partner and stand up very straight, as if 'at attention,' then bend just your neck to look at the floor. Your partner will see your C7 vertebra and put their finger on it. Now straighten up.
- Your partner will now measure from the center of your waistband up to the C7 vertebra. This is your Torso Length, which will translate roughly as 16-18 inches Small, 18-20 inches Medium, 20-22 inches Long. Many packs have adjustable suspension systems, but if you can't find your size, you want to go up, not down.
Before heading out to try on packs, consider your outfit. The shoulder straps and hipbelt of your pack will create pressure points, and to be comfortable, you'll want to reduce the bulk and seams in those areas. Classic 'backpacking' shorts and trousers have a very smooth waist area with no belt loops, and may have an integrated flat web belt. For the upper body, fewer layers will be cooler, but an undershirt and long-sleeve button-down in a synthetic blend will give you a better comfort adjustment options as well. The closer you can get to this ideal outfit for the pack fitting, the better sense you'll have of how it will feel on the trail.
When you find a pack in the volume and size you're looking for, take a quick tour by opening every zipper, looking in all the compartments, checking out all the load control straps on the pack bag. When you get to the suspension, flex the hipbelt and shoulder straps, taking special note of the sternum strap and 'load lifters' on the shoulder straps and stabilizer straps on the hipbelt. Make sure all of these are loose before proceeding with the fitting.
The shoulder strap yoke will adjust up and down using a buckle and strap and/or Velcro fastening, and while the hipbelt may be replaceable and have pivot points, it will be in a fixed position. Most strap-based torso adjustment systems will be anchored behind a pad in the middle of the hipbelt and should have an obvious handle or opening. Velcro may be used on the shoulder strap assembly between the back panel and pack bag and can be tricky to separate the first time. Don't be afraid to get a little rough - the backpack is designed to take some abuse.
After figuring out where things are, don't make any adjustments, just put the empty pack on. For this first, or 'cold' fit, just get the hipbelt placed correctly, with the iliac crest centered vertically on the padding so it is wrapping around the bone, buckle centered and snugged down. Then tighten the shoulder straps, but only to the point where you can feel the back panel make contact. Connect the sternum strap and adjust it vertically for comfort but keep it slack. When seen in profile, with no weight in the pack, the shoulder straps should be angled upward at about 45 degrees to meet the pack. Make a note as to how far up or down the shoulder straps must be adjusted, and loosen the shoulder straps and hip belt, then take the pack off.
This is where the shop staff can speed up the process, but you will still need to know how to adjust the pack, since only you will be making adjustments in the field. With the pack on the floor, make whatever adjustments are necessary, then grab the test weights. Usually cloth bags of beans and/or stuffing designed to emulate gear, they are essential in getting the best fit before you get the pack home. If the shop doesn't have weights, make sure to keep the tags when you get home and really pack the bag.
The bottom of the bag is traditionally where the sleeping system is packed since it is bulky but not especially heavy, so place similar stuffing in the bottom of the pack bag. Place the heaviest and densest part of your load on top of the sleeping system/stuffing against the back panel, centered and close to your center of gravity. Place lighter items around to keep everything more or less where it belongs. You should follow this same approach when loading the pack with gear, because the closer the weight is to your center of gravity, the less energy you will expend just moving and staying upright. You want the pack moving with you. With a load similar or a bit heavier in weight to what you will be carrying, put the pack back on, again adjusting the hipbelt first, then the shoulder and sternum straps, but leave everything else alone.
With the pack weighted, the shoulder strap should now come off the shoulder and be level (parallel with the ground) to where it meets the pack. If it is curving down or angled up, remove the pack and adjust.
Take a stroll around the store, covering at least a dozen strides with a couple turns. Stand on one leg, dance a bit, get a feel for how you and the pack are moving. Without making any significant adjustments, the bag will be pretty floppy. When you return to where you started, you can fix some of that.
On the sides of the hipbelt where it meets the pack bag, you should find the hipbelt stabilizer straps. By tightening these, you will pull the bottom of the bag up and in, firming up the link between you and the bag. Be careful that the hipbelt is pretty snug before making this adjustment, as it can compress the hipbelt and cause a 'corner' to form, especially when the stabilizer is tight before the hipbelt is put on.
Next, place your fingers on the shoulder straps at the top of your shoulder. You'll feel the 'load lifter' strap as it separates from the shoulder strap. Follow it up to the buckle on the pack bag. Find the end of the webbing and pull, keeping the adjustment even. These are called 'load lifters' because they can relieve or lift any pressure (load) you feel on the top of your shoulder, shifting the strap contact point to the front of your shoulder. The load lifter essentially changes the arc of the should strap from hipbelt-around-to-scapula to hipbelt-up-to-ear. In profile, there should now be a gap on top of your shoulder.
Do the stroll again and feel how much more comfortable the pack is now. To check the overall fit, loosen the shoulder straps. You should feel the weighted pack pivot on the hipbelt, indicating that most of the load is being directed to the legs and the shoulder straps are just keeping the pack under control. If it shifts downward, increasing the load on the hipbelt, the straps were too tight.
The final adjustment is most notable if someone else does it while you are wearing the weighted pack, but you can also do it yourself with the pack on the floor with the same effect. Go around tightening the vertical lid straps and all the horizontal and/or diagonal load control straps on the pack bag, shrinking the volume down until the load cannot move or shift on its own. The bag may not feel lighter, but it should be more compact and more responsive to your dance moves, which will equate to increased confidence on the trail and less energy wasted compensating for feeling off-balance.
Reverse the adjustments any time you empty the bag or change the load significantly. By loosening and readjusting each time, you make sure the fit is the best it can be. With practice, it will become second nature and you'll tweak your pack on the fly, finding the best settings for various loads and conditions.