1. One pound on your feet equals five pounds on your back.
This old backpacking thumb rule holds true, according to a 1984 study from the U.S. Army Research Institute. They tested how much more energy was expended with different footwear (boots and shoes) and concluded that it take 4.7 to 6.4 times as much energy to move at a given pace when weight is carried on the shoe versus on the torso.
In practical terms, this means you could carry half a gallon more of water (a little over 4 pounds) if you buy boots that are a pound lighter, which isn’t hard to do; and that’s a lot of water. Now imagine the energy savings of backpacking in light trail running shoes rather than heavy, leather backpacking boots over the course of 7-day backpacking trip.