The human eye is really good at dividing things in half, so it's easy to make power-of-two divisions without special tools. Just divide whatever it is in half,

The human eye is really good at dividing things in half, so it's easy to make power-of-two divisions without special tools. Just divide whatever it is in half, then divide it in half again, and so forth until you have a sixteenth. The US system has lots of power-of-two factors in it, which suggests that it was born in the marketplaces and workbenches of people who did most things by hand, rather than our modern world where we design everything on paper first.