Types
Unloaded backpack weight varies by pack type. The lightest hydration packs can weigh as little as 7 oz. Day packs range from an ultralight 20 oz. to as heavy as 3 lb.
Internal frame overnight and extended trip packs can weigh as much as 5 to 7 lb. These packs are generally too heavy and bulky to justify using with light loads under 20 lb.
Features
Certain backpack features can add weight to even the smallest designs. Material thickness and padding is probably the most common heavy addition to small packs. Ultralight 7 oz. packs are usually made of extremely thin nylon and are not very tear-resistant. Sometimes a thicker, resilient nylon shell can be worth an extra 5 or 6 oz.
Frames also add a significant amount of weight to packs. Modern designs are reducing this cost, however, and the stability of a frame is necessary with large loads.
Other small features may contribute to weight. Bulky zippers, nylon webbing loops and built-in rain covers can all add ounces or even pounds to a pack.
Function
While the unloaded weight of a pack is determined by its design, the load depends on its function. This can change depending on whatever adventure you happen to be taking.
Short day hikes or runs may require only water, food and a few tools in an ultralight pack, totaling 3 to 5 lb. For a longer day, you'll need more water and food, and possibly extra clothing. In a larger pack, this may mean a load of up to 12 lb.
Longer trips add food, shelter, cookery and miscellaneous gear. A summer overnight trip may require only 15 lb. of gear, while 3 or 4 nights might need 20 to 25 lb. Normally, weight increases from this point because of extra food and clothing needed.
Specialized climbing or cold-weather treks will add a large amount of gear to your pack. A weeklong winter trek can easily put 50 lb. in your backpack.
Size
Many packs include ratings that detail how much weight they can comfortably support, but you should still know how large a pack must be to carry your load.
Day packs to 2,000 cubic inches can often carry loads as heavy as 20 lb., though smaller, frameless packs can handle only 10 or 15 lb. A small, 2,500-cubic-inch overnight pack can easily hold 20 lb., and a larger 4,000-cubic-inch backpack can carry nearly 30 lb. of gear.
To carry large loads of 30 to 50 lb., you will probably need a pack with a capacity of at least 5,000 cubic inches.
Expert Insight
Just because a backpack will hold a certain amount of gear does not mean that it can handle the weight. Particularly in ultralight packs, thin material and loose construction can cause a strap to fail under stress. Make sure your pack can stand up to the weight you plan to put into it, as well as any possible trauma that it may get on the trail. Rocks, water and tree branches can all undermine a pack's strength. If in doubt, look for a sturdier pack to carry your gear.
