Busting Myths about the Metric System


This week is the 41st anniversary of the Metric Conversion Act, which was signed on December 23, 1975, by President Gerald R. Ford. Normally, we celebrate by sharing metric education resources, but this year I want to use the occasion to dispel some common misconceptions about the U.S. relationship with the metric system.

You’ve probably heard that the United States, Liberia and Burma (aka Myanmar) are the only countries that don’t use the metric system (International System of Units or SI). You may have even seen a map that has been incriminatingly illustrated to show how they are out of step with the rest of the world.

Countries which have not "officially" adopted the metric system (The United States, Myanmar, and Liberia) in gray. By →AzaToth [Public domain], via Wikimedia Commons

Countries which have not “officially” adopted the metric system (The United States, Myanmar, and Liberia) in gray. By →AzaToth [Public domain], via Wikimedia Commons

It’s a compelling story and often repeated, but you might be surprised to learn that it’s simply untrue!

While it’s true that metric use is mandatory in some countries and voluntary in others, all countries have recognized and adopted the SI, including the United States.

Dr. Russ Rowlett at the University of North Carolina at Chapel Hill emphasizes on his website that becoming metric is not a one-time event but a process that happens over time. Every international economy is positioned somewhere along a continuum moving toward increased SI use. There are still countries that are amending their national laws to adopt mandatory metric policy and others pursuing voluntary metrication.

The Unites States was one of the original countries to sign the Treaty of the Meter in 1875, which is now celebrated annually on May 20, World Metrology Day. It’s been legal to use the metric system since 1866, and metric became the preferred system of weights and measures for U.S. trade and commerce in 1988.

Metric system use in the US lies along a continuum where some measures are entirely in metric and others are entirely devoid of it, at least at the consumer level. Credit: E. Gentry/NIST

Metric system use in the US lies along a continuum where some measures are entirely in metric and others are entirely devoid of it, at least at the consumer level. Credit: E. Gentry/NIST

·        We use the SI every second of every day. After all, the second (s) is the SI base unit of time.

·        U.S. coins & currency are produced using metric specifications.

·        Many U.S. products, like wine and distilled spirits, have been successfully sold with only metric measures since the early 1980s.

·        Metric units are used extensively on packages to provide net quantity, nutrition and health-related information, and for prescription drugs, over-the-counter medicine, vitamin supplement dosing, and other consumer products.

It’s impossible to avoid using the metric system in the United States. All our measurement units, including U.S. customary units you’re familiar with (feet, pounds, gallons, Fahrenheit, etc.), are defined in terms of the SI—and mass, length, and volume have been defined in metric units since 1893! The SI’s influence is pervasive and felt even if most people don’t know it. I envision U.S. metric practice like a huge iceberg. Above the water’s surface, U.S. customary units appear to still be in full effect. In actuality, below the water’s surface we find that all measurements are dependent on the SI, linked through an unbroken chain of traceable measurements.

Although U.S. customary units are still seen alongside metric units on product labels and merchandise literature, it’s common for the goods themselves to be made using SI-based manufacturing processes. Why? While some businesses are concerned that consumers expect to see customary units on the package, when it comes to manufacturing processes, they are under constant pressure to stay competitive. Adopting the latest science and technology, developed using metric design practices, enables innovation. In addition, many industries extensively use international supply lines to develop, manufacture, and sell their products around the world.

I’m the coordinator of NIST’s Metric Program. Because of my passion for all things metric, I encourage companies to investigate adopting metric practices whenever possible and show them how doing so can make a strategic economic impact for their organization. Changes in technology and extremely competitive domestic and global marketplaces can compel businesses with little previous experience to explore metric use. Many have found that going metric pays off, resulting in a competitive advantage.

Going Metric Pays Off
During the recent recession, lumber companies located in the U.S. Northwest saw their U.S. customer base shrink, but their Canadian and Japanese markets, both of which use metric, expand—especially after the 2011 earthquake and tsunami. Wood-product producers made adjustments so that their production systems could flex between metric and U.S. customary measures based on what their customers needed. Because so much of the world uses metric only, more and more U.S. companies are recognizing the benefits of metric as they find new international markets for their products.

If your business is considering making the switch to metric, I would encourage you to conduct small beta tests to explore how your customers react. Research can help ensure decisions aren’t based on out-of-date information or preconceived notions. You might be pleasantly surprised by how quickly customers adapt—and how using metric benefits the bottom line.

And as always, if you need advice, be sure to give NIST a call; we’re here to help!

*Updated Dec. 28, 2016


About Author

Elizabeth Gentry

Since becoming Metric Coordinator in 2005, Elizabeth has worked to support voluntary conversion to the International System of Units (SI), commonly known as the metric system, in the U.S. In addition to providing information and assistance to federal, state and local weights and measures officials, business, industry, educational institutions, and the public concerning the SI, she also identifies opportunities for increasing its understanding and use in trade and commerce. When she’s not extolling the virtues of the converting to metric, she enjoys hiking with her 60 kg Rottweiler, Matilda.


  1. I like the “metric continuum” but I think the lightbulb might be misplaced on it. It is designed to operate on a certain voltage (volts), draw a certain amount of power (watts), produce a certain amount of light (lumens) at a color temperature (kelvin) and do so for a certain lifetime (hours). The common screw base (E26) is designated by its diameter in millimeters. Only the bulb diameter is in eights of an inch (A19 for common household bulb). My remarks largely apply to other bulb styles as well.

    I would move it up two notches, certainly at least one. In fact, neither the electricity used nor the light produced can be measured in Customary as Customary has no such units.

  2. The wife and I were traveling through NY and Canada the day Canada made the change, I’m of the opinion that the common man (American) is just to hardheaded to change everyday life to METRIC?? (not invented here)

    • Elizabeth Gentry
      Elizabeth Gentry on

      Although none of the modern measurement systems were invented in the U.S., our role as an original signatory to the Meter Convention established our commitment to improving measurements that’s guided the journey towards a coherent system based on fundamental constants, rather than barleycorns, Roman soldiers paces, or His Royal Highness’ body parts.

      The old British system was a hodgepodge of units, assembled from a variety of cultures and sources. U.S. colonists brought it here; but subsequent changes over time created additional differences between the British and U.S. Customary systems.

      But that’s another blog article!

      NIST HB 44 Appendix B (2.3) https://www.nist.gov/sites/default/files/documents/2016/11/10/appb-17-hb44-final.pdf) explains how the U.S. Customary System differs from the British System.

      NIST SP 447 Weights and Measures Standards of the United States, A Brief History (https://www.nist.gov/sites/default/files/documents/pml/wmd/pubs/2010/12/16/sp-447-2.pdf) offers a more detailed explanation.

      • Daniel Jackson on

        The US failed to metricate in the ’70s mostly due to a misapplied sense of arrogance. Thinking one is better than everybody else can cause one to make bad and irrational decisions. Decisions that can come back to haunt you generations later or when your industries that would like to change can’t find local talent with a proper metric functionality and are forced to close shops in the US and go elsewhere where the metric system is first nature or the only nature among the populations.

        Like any profitable business, metrication should have been achieved by strong leadership, a well devised plan, extensive education, and a system of punishment for any resistance. All of this could have accomplished a completed metrication by now with no one looking back.

        The NIST and Congress both failed the nation. The NIST could have applied more pressure on the congress and the congress should have set the standard as their right per the constitution and even if initially unpopular in the best interest of the nation for the present and future generations.

        But it isn’t too late. The NIST really needs to rise up and present the congress with a timely workable plan and push until the job is done. It will be a sacrifice, but nothing good comes from stagnation and going in reverse. Pay now or pay later. The choice is yours to make.

      • In fact, they are the British (pre-Imperial) units in use at the time of the Revolutionary War. The US gallon and bushel were defined by British Parliament circa 1700. We incorporated none of the improvements of the 1824 Imperial Act. Not quite the “freedom units” some Americans like to imagine.

      • Daniel Jackson on

        What is most interesting is that the origin of USC is Roman. The Roman influence in Europe established the ancestors of USC and imperial. The British before the Norman invasion used a decimal system with the wand as the fundamental length unit equal to about 1007 mm.

        Some British traditionalists oppose the metric system on the false belief it was forced on them by EU regulations when it fact the British actually invented it and left their mark heavily upon it.

        After the Norman invasion, the Norman yard replaced the British wand (metre) to the point that the wand in its last days as the yard and the hand.


        See metrology.

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