If you are dealing with the military, the question of how much should your backpack weigh, has been answered by years of experience. But remember they are dealing primarily with young healthy males. In the Army and Marines training often consists of hiking at a fast pace over rough terrain with a backpack weighting at least 45 lbs. In addition, they will also carry a weapon, wear boots, BDU (Battle Dress Uniform) , LBE (Load Bearing Equipment, ammunition, canteens of water, and a helmet. Depending on your job, your total load for combat can be 95 pounds or more.
Now we have a very different problem, most of us are not in great shape, have young children or are getting long in the tooth. So what should our backpack weigh? There are several factors that affect the weight we can carry. These include the pack weight itself, the physical and mental condition of the packer, as well as the terrain and conditions in which one is traveling.
Physical variables, include fitness, build type, bone and muscle density, the health of your joints (knees in particular), and age, these will change the answer for each person.
Guidelines used by recreational backpackers are that an individual in good health should be able to carry about 20% of their body weight, a 40 lb pack for a 200-pound person. More experienced backpackers should be able to carry 25% of their body weight, a 50 lb pack for a 200-pound person. Very experienced and well-conditioned backpackers can carry 35% of their body weight – a 70 lb pack for a 200-pound person.
Age and sex can affect the above suggested weights, a doctor told me that most men in their 70’s should not carry over 20 lbs for any long distance. Children are another problem and you as parents will have to make the decision on how much weight they can carry. Women often lack the upper body strength of men and cannot carry as much weight.
Backpacks can damage your health, if they are more than your personal limit. So start with lighter loads and short trips, and gradually increase your backpack weight and the length of your trips. Remember that with very heavy backpack you need to be careful to put it on right, otherwise you can damage your back before you even start to walk.
The bottom line is that each person is unique and you should spend time discovering for yourself how much should your backpack weigh?