Why isn't the U.S. on the metric system?
http://science.howstuffworks.com/why-us-not-on-metric-system.htm
"Many myths swirl around the metric system and U.S. involvement with it. Let's dispel a few."

You know what the rest of the world has figured out? The metric system. It's time the US got on board.
http://blogs.scientificamerican.com/plugged-in/2013/08/20/you-know-what-the-rest-of-the-world-has-figured-out-the-metric-system-its-time-the-us-got-on-board/
"I've met a lot of people and learned a lot while traveling Europe the past several weeks. Of all the things I have had to explain to fellow travels as not only an American - but a Texan - by far the most frustrating thing is our stubborn refusal to embrace the metric system."

It's the Science, Dummy: Why Americans Hate the Metric System
http://www.stuffyoushouldknow.com/blog/its-the-science-dummy-why-americans-hate-the-metric-system/
"We Americans are known for our strong sense of national pride toward our unreasonable stubbornness against adopting the metric system. We haven't always been so intractable toward what has become the international standard for measuring distance, mass, temperature and other things we need to describe to one another from time to time."

A Brief History of Measurement Systems
https://standards.nasa.gov/history_metric.pdf
"Weights and measures were among the earliest tools invented by man. Primitive societies needed rudimentary measures for many tasks: constructing dwellings of an appropriate size and shape, fashioning clothing and bartering food or raw materials."

The Metric System in the United States
http://www.unc.edu/~rowlett/units/usmetric.html
"Article I, Section 8 of the U. S. Constitution gives Congress the power to "fix the standard of weights and measures" for the nation. The First Congress, meeting in 1789, took up the question of weights and measures, and had the metric system been available at that time it might have been adopted. What actually happened is that Thomas Jefferson, who was then serving as the first Secretary of State, submitted a report proposing a decimal-based system with a mixture of familiar and unfamiliar names for the units."

How the Metric System Works
http://science.howstuffworks.com/metric-system.htm
"Before there were global supply chains and trade agreements, convenience was the highest priority when it came to measurement. In most cases, people didn't have access to sophisticated measuring devices, so they relied on body parts, which were easy to carry around and offered somewhat consistent results."

5 Things You Didn't Know About the Metric System