Back when I was a Catholic-school kid in northern Wisconsin, my school lessons briefly focused on the metric system. This was in the late 1970s. Along with learning cursive and the referents of rosary beads, we learned that the base-10 system would be critically important in all things science and engineering.
This focus on metric stemmed from the Metric Conversion Act, passed in Congress in 1975, and the United States Metric Board that it created. Forward-thinking members of Congress and President Gerald Ford wanted us kids to join the rest of the world in thinking about distances in kilometers and weight in kilos. Signing the bill in December 1975, Ford argued that our continued use of U.S. customary (the more accurate name for what’s sometimes the called the British Imperial system) had created “an island in a metric sea.”
But this well-intentioned legislation had a problem: It made the change to metric, in the words of the act, “completely voluntary.”
So after a brief burst of attention to metric, many of us pretty much forgot about it, except when running a 10K or buying a 2-liter bottle of soda. President Ronald Reagan disbanded the Metric Board in 1982.
But in reality, metric never really left. As Elizabeth Benham pointed out in her article for the National Institute of Standards and Technology, U.S. customary units have been defined in terms of metric units since 1893. And even though the progress has been slow, the U.S. has continued toward conversion, as Ross Rowlett described in his short history of metric in the U.S. Indeed, numerous manufacturers, including Caterpillar, Ingersoll-Rand, and General Motors, have adopted metric to facilitate their participation in the global economy.
Now that I work at Howe’s Welding and Metal Fabrication, a small welding and metal fab shop in Ames, Iowa, this country’s failure to fully adopt metric frequently manifests in my life. Most of Howe’s clients—local people, businesses, and municipalities—use U.S. customary when they bring in a hand-drawn sketch or a CAD drawing. They specify dimensions in feet, inches, and fractions of an inch. But not all of them do. Rethreading a bolt hole in a John Deere component, for example, requires a metric pitch, as opposed to the threads per inch of U.S. customary.
So at Howe’s, we have to oscillate between the two systems, sometimes tackling projects that involve converting between the two. In those moments, the additional mental effort, the greater potential for error, and the additional costs of the U.S,’s two-system obstinacy become obvious. One comment on the machinist subreddit clarified this craziness: “I’m currently working on a mounting plate that’s 4.5 by 8 in. that needs a 40 mm bore 1/2 -in. deep located 75 mm from the edge with m10 tapped holes and two 1/4-20 set screws tangential to the bore. Please kill me.”
Pat Naughtin, an expert on metrication and the author of the newsletter Metrication Matters, once attempted to calculate the cost to the U.S. of maintaining the status quo. Acknowledging the complexity of the task, he estimated in 2008 that the cost is in the ballpark of $1.28 trillion dollars per year (about $1.86 trillion in 2025). These losses stem, as he wrote in another essay, from mistakes caused by conversion errors, buying and maintaining two sets of inventory, lost time teaching two systems, and jobs lost when international companies avoid working with U.S. companies still using U.S. customary, among many other problems.
And so the super-slow progression of the U.S. toward metric and away from U.S. customary continues. More companies switch, taking a financial hit in the short term for big savings in the long term. More employees at those companies become familiar with millimeters and grams. More U.S. school kids gain familiarity with metric in science courses. And more Americans travel abroad and perceive the value of a shared system (even if they still think Fahrenheit is better).
In the meantime, I add and subtract fractions of an inch, cursing the 94th U.S. Congress for its lack of gumption.