Why the US hasn't fully adopted the metric system

Democratic presidential candidate and former Sen. Lincoln Chafee (D-RI).
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Every election cycle candidates promise to go the extra mile, but this season only one is promising to go the extra kilometer.

In his announcement speech for a 2016 presidential bid, former Rhode Island Gov. Lincoln Chafee threw his support behind a cause that has Americans, both Democrat and Republican up in arms: Converting to the metric system.

"Here's a bold embrace of internationalism: let's join the rest of the world and go metric," Chafee said. The only problem with that stance though, is that many voters hold our system of measurements to be a long-standing pillar of American individualism. (Tweet This)

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But few know the U.S. has already technically adopted the metric system.

"The metric system has been legal in this country since 1866," Don Hillger, president of the U.S. Metric Association, a non-profit that battles for nation-wide metric conversion, told CNBC. "I wish we saw it out of a more popular candidate... but we're not going to win the battle on popularity, its a logic thing."

So why don't we use the metric system?

Indeed, the U.S. is the only industrialized nation that has yet to widely convert to the metric system. In fact our refusal to convert our own measurements dates back to the very creation of the country.

Though colonists were accustomed to the Imperial system of measurements used by the British, early founders introduced their own tweaks under the Constitution's Article I, Section 8 that states Congress holds the power "to coin money...and fix the Standard of Weights and Measures." Despite calls to convert in 1821, Secretary of State John Quincy Adams saw no need, and affirmed America's metric system snub.

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But in 1866, President Andrew Johnson committed an act of treason in the eyes of the measurement community by signing into law an act of Congress that made it "lawful throughout the United States of America to employ the weights and measures of the metric system in all contracts, dealings or court proceedings." But even that couldn't kill the U.S. customary system. Neither could the push to convert in 1975 when Congress passed a similar Metric Conversion Act. Nor would our stubborn measuring ways die with the Trade and Competitiveness Act of 1988.

The reason why is that all of the measures passed by the government have been voluntary. Even states and counties have the right to use either measurement system as they please. A stretch of Interstate 19 known as the "Metric Highway" in Arizona has featured metric units on road signs since the '80s. The laws are similarly voluntary on the part of American producers. The only mandate comes from the Food and Drug Administration which requires dual labeling, according to Don Onwiler, executive director of the National Conference on Weights and Measures—a group that has helped keep consistent measuring standards across states since 1905.

"I don't even know how you would estimate the cost to convert, but it would be a costly process. Our position is we want to remove the barriers so where it's practical it can happen naturally," he said. How practical and necessary a conversion would be can vary from industry to industry.

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NASA claims its costs to convert its measurement systems would be over $370 million. But not converting has costs of its own. NASA lost $125 million when its Mars Climate Orbiter was destroyed after its altitude-control system mixed up U.S. customary units with metric units.Other industries and the public could face different conversion costs.

Hillger insists the costs are worth it in the long run. "We realize there is a cost with going metric, like changing street signs," he said. "But those costs are in short term, the benefits last far longer."

For Lincoln Chafee, those benefits could last four years in the White House if Americans agree with his call to convert. If, that is, he can convince them to give an inch.