The real reason the US doesn't use the metric system

Is it so simple as this? Is this the petulant reason why the US doesn't use the same universal system of weights and measurements — the metric system — that nearly every other country in the world uses? Everyone except Myanmar, Liberia, and, yes, the United States of America. Pure obstinacy and an unwillingness to hear over the sound of our own "freedom"? ("U! S! A!") But wait. The United States has adopted the metric system, you say? Back in 1866, via the Metric Act, as Smithsonian Magazine relates. It remains unenforceable, however, and now people are confused because they can drink half-liter bottles of water while running a 5k, and then travel 2.3 miles home and use two cups of flour to make some sweet, sweet blueberry pancakes.

Time to clear up the confusion, folks. The real answer about why the US doesn't use the metric system is of course a bit more complex. We all know that the metric system is easier: measurements are separated by decimals, which means things are divided into 10ths, 100ths, and so forth. 1 kilogram of weight? 1,000 grams. 1 gram? 1,000 milligrams. Same thing for length (meters) and volume (liters). Could it be any easier? Surely, it makes more sense than 12 inches = 1 foot. (Whose foot, exactly?) To get to the bottom of this mystery, we have to time-travel and have a chat with good ol' Thomas Jefferson. 

Pirates captured Jefferson's friend's ship and botched the conversion to metric

Thomas Jefferson (Secretary of State in 1790) was a huge Francophile. Remember at this point that France gave the US a tremendous edge in the American Revolution when they joined our side in 1778, as Battlefields states. They provided money, troops, naval support, and military leadership, without which it's far less likely that the fledgling "United States" would have won independence from its English overlords across the pond. This happened during the French Enlightenment, or Age of Reason, as outlined on Alpha History, a period of intense philosophical and political development that resulted in France's own revolution to overthrow its monarchy in 1799. 

Leading up to this time, there was ongoing debate in France about overhauling its system of weights and measurements, which used time-honored, agrarian terms like journée ("day") to measure field size, and boisseaux ("bushels") to estimate how many seeds were needed to sow a field. Leading French thinkers wanted a unified, "enlightened" system of measurement, and Jefferson was all about convincing Congress to jump on board as well. He asked his buddy, Joseph Dombey, over in France, to bring a copper cylinder (an exact kilogram) to the US to use in a demonstration to convince the powers that be to adopt the newly christened "metric" system.

And then, guess what? You got it: pirates. They captured Dombey's ship and took him prisoner, per the Washington Post. Dombey never arrived, and Jefferson's proposal sank.

Just too expensive and too troublesome to change

Since then, debates about whether or not, and how, the US should completely adopt the metric system — officially named the International System of Units (SI) — haven't really stopped. As recently as the 1970s, as Time states, there was a huge push in schools to accept the inevitability of the metric system, and, well ... people don't change too easily, do they? The current US Customary System, as it's called, is itself based on the medieval-rooted British Imperial System held over from the Revolutionary War days. It has stayed in use because it got prohibitively expensive and troublesome to change, per How Stuff Works. The spread of America's industrial manufacturing complex of railroads and steel, measured using the old system, made changing especially tough.

Section 8 of Article 1 of the US Constitution explicitly states that Congress has the power to "fix the standard of weights and measures," per Britannica. And in addition to the aforementioned Metric Act of 1866, Congress did indeed pass the Metric Conversion Act in 1988, stating that the metric system was the "preferred system of weights and measures for United States trade and commerce," making it mandatory for federal agencies to use "the metric system of measurement in its procurements, grants, and other business-related activities." Some industries, like the pharmaceutical industry, have followed suit; others haven't.

Until that inevitable (perhaps) time comes, feel free to chant U! S! A! all you'd like.