After the French Revolution in the late 18th century, the fledgling French republic devised a new unit of measurement called the “meter”—one ten-millionth of the distance between the North Pole and the equator. That became the basis for the metric system, which was eventually adopted in many other countries around the world.
The U.S. wasn’t among them. Though Thomas Jefferson did show interest in the system when he was secretary of state in the 1790s, no change ever came to fruition. According to Northwestern University history professor Ken Alder, Americans may have simply been resistant to the idea of standardizing something on a global scale. “I understand when people resent it as a remote force of globalization that produces uniformity, and it's perfectly rational to want local control,” he told Live Science. “It can also be about taking a position against something that's hyperrational and French.”
Furthermore, Britain’s Industrial Revolution began to take hold in the U.S. during the 1800s, and most manufacturers were calibrating machinery and measuring products using inches, pounds, and all the other familiar units of Britain’s imperial system. As Encyclopaedia Britannica explains, shifting to the metric system would’ve been laborious and costly; whenever Congress brought it up, business owners and citizens quickly shut it down. Two centuries later, those same issues continue to keep the U.S. from committing to the metric system.
That’s not to say we haven’t tried. In 1975, Congress passed the Metric Conversion Act, which encouraged businesses to transition to metric units of measurement. Since it wasn’t mandatory—and imperial units would still be accepted—it hardly upended the status quo. Later that decade, President Jimmy Carter spearheaded a campaign to swap miles for kilometers on road signage, but that didn’t stick, either.
Alder pointed out that France was probably only able to implement a whole new system because the country was in a state of complete upheaval at the time, and many other old processes were changing, too. Britain was also undergoing a large-scale political renovation when it finally switched to the metric system in the 1970s. Because the U.S. government has been relatively static since the formation of the Constitution, we haven’t had a similar opportunity.