150 Years of Legal Metric Usage in the USA

UKMA is nothing if not internationalist in its outlook. So today, 28 July 2016, we celebrate a significant anniversary for the use of the metric system in the USA. It marks 150 years of legal metric usage in the USA.

Here, we present a timeline from 1866 to modern times.

1866 – The Metric Act of 1866, enacted 28 July 1866, legally recognized the metric system of measurement in the US. It’s sometimes referred to as the Kasson Act, after Congressman John A. Kasson of Iowa, who chaired the House Committee on Coinage, Weights, and Measures. It stated that “no contract or dealing or pleading in any court, shall be deemed invalid or liable to objection because the weights or measures expressed or referred to therein are weight and measures of the metric system.”

1875 – Seventeen nations, including the USA but excluding the UK, signed the Convention of the Metre on 20 May 1875. This treaty set up the International Bureau of Weights and Measures (BIPM) to maintain common world standards for metric measurements.

1889 – The Convention of the Metre had provisions for providing its signatories with a prototype metre and kilogram. As a result, the USA, the UK and the other signatories to the Metre Convention each received a prototype metre and kilogram for maintaining agreed measurement standards. Congress supplied each state with copies of the national prototype metric standards.

1893 – The Mendenhall Order defined the yard, pound and other US customary units in terms of the metric system. It fixed conversions for the yard at exactly 3600/3937 metres and the avoirdupois pound at exactly 0.4535924277 kilograms. US measurements for mass and distance have been fixed in terms of metric units ever since.

1894 – Congress passed a law that required all medicine prescriptions to be expressed solely in metric units. This law came into force on 1 January 1895.

1916 – Establishment of the US Metric Association, originally called the American Metric Association, a non-profit organisation that advocates the full adoption of the metric system throughout the US.

1920 – USMA published its first metric style guide. The current version of this guide is now called “Guide to the Use of the Metric System (SI)”.

1954 – The USA adopts the International Nautical Mile, replacing the older US nautical mile. The International Nautical Mile is exactly 1852 metres.

1958 – A conference of English-speaking nations, including the USA, standardised the precise quantities of the yard and pound in terms of the metric system. They agreed that one avoirdupois pound would be exactly 0.45359237 kilograms and one yard would be exactly 0.9144 metres.

1964 – The National Bureau of Standards (NBS), now known as the National Institute of Standards and Technology, standardised on the use of the metric system “except when the use of these units would obviously impair communication or reduce the usefulness of a report.”

1966 – The USMA Metric Today newsletter was first published.

1967 – The Fair Packaging and Labeling Act (FPLA) was made law.

1968 – Congress authorised a three-year US Metric Study, to investigate increasing metric use in the USA and feasibility of metrication. This study was carried out by the National Bureau of Standards (NBS).

1971 – At the end of the three-year US Metric Study period, the US Secretary of Commerce reported its findings to Congress and recommended that the US change to predominant use of the metric measurements as part of a ten-year national plan.

1973 – The American National Metric Council (ANMC) was created as a not-for-profit trade organisation to help US industry to switch to the International System of Units (SI), also known as the modern metric system.

1974 – The Education Amendments of 1974 (Public Law 92-380) encouraged educational agencies and institutions to teach the metric system to students as part of their normal education.

1975 – The Metric Conversion Act was signed into law by President Gerald Ford. This Act set up the US Metric Board to help and advise on increasing the use of the metric system. It was based entirely on the voluntary adoption of the metric system and had no mandatory powers.

1976 – The National Council of Teachers of Mathematics (NCTM) introduced the tradition of National Metric Week. The first one was during the week of 10 May 1976 and there has been one each year since then.

1979 – The Treasury Department’s Bureau of Alcohol, Tobacco, and Firearms (BATF) introduced requirements for wine to be sold in 7 standard metric sizes (i.e. based on millilitres and litres).

1980 – The Treasury Department’s Bureau of Alcohol, Tobacco, and Firearms (BATF) introduced requirements for distilled spirits to be sold in 6 standard metric sizes (i.e. based on millilitres and litres).

1982 – The US Metric Board was abolished.

1988 – The Omnibus Trade and Competitiveness Act was enacted. This law amended the Metric Conversion Act of 1975 and declared the metric system to be the “preferred system of weights and measures for US trade and commerce”.  This was signed into law by President Ronald Reagan. This law instructed federal agencies to use the metric system in procurement, grants, operations and business dealings by the end of 1992.

1991 – President George H. W. Bush signed Executive Order 12770, Metric Usage in Federal Government Programs. This order directed government departments and agencies to use metric units as the “preferred system of weights and measures for US trade and commerce”.

1994 – The Fair Packaging and Labeling Act (FPLA) was amended to add a requirement for metric units on most consumer products.

1996 – The Savings in Construction Act amended the Metric Conversion Act of 1975 to define specified terms, including hard-metric. This Act contains provisions for the metric usage in construction projects procured by federal agencies and for the use of hard-metric versions of specifications with these projects.

2004 – The Department of Energy High-End Computing Revitalization Act amends the Metric Conversion Act of 1975 and the Savings in Construction Act of 1996 to repeal the expiry date of federal agency authority to require metric system specifications.

2008 – The National Institute of Standards and Technology (NIST) published the Interpretation of the International System of Units for the United States.

While significant progress has been made over the last 150 years towards the use of the metric system in the USA, they are still far behind the UK in terms of the metric transition. Like the UK, the USA has also tried the voluntary approach to metrication. In both countries, this has led to a measurement mess with no end in sight. The British and Americans are now stuck between two incompatible competing systems (or three if you distinguish between Imperial and US Customary) and there is a reluctance by any political leader to take bold decisions to complete metrication.



5 thoughts on “150 Years of Legal Metric Usage in the USA”

  1. Thank you for this high-level timeline of metrication in the USA. Indeed, we would be much farther along the road to metrication over here if we were at the same point the UK is (though I hardly recommend muddles of any type!)

    I do believe the younger generation of Americans is much more open to metrication than many older folks are. If the Democrats retain the White House this November and retake the Senate (and maybe even the House, if you believe in miracles), there is certainly a chance to amend the FPLA to allow for metric-only labeling. That would be a first step towards raising metric awareness among Americans of all stripes.

    And who knows? Maybe with such an outcome in November the Federal government would be bold enough to start a conversion process much like the one pursued in Australia. As Barack Obama would say: I believe in the audacity of hope! 🙂


  2. That is a great summary.

    A few points which may be of interest:
    1967. The original FPLA required Customary units, but allowed metric as supplemental. As you note, “dual” became a requirement for most pre-packaged goods in 1994.

    1988. The Omnibus Act unfortunately also established as policy that US metrication must be voluntary.

    1996. The Savings in Construction Act also unfortunately required consideration of Customary-sized bricks and lighting fixtures, if they were less expensive. That obviously causes problems in modular metric design, mostly leaving Federal metric construction as an exercise in conversions.

    2008. This version of NIST SP330 was published as the US version of the 7th edition of The SI Brochure. NIST has previously published, under the same title and publication number, versions to agree with earlier editions of the SI Brochure (I have the 2001 edition which agrees with 6th ed. SI Brochure). It has also published short summaries in the Federal Register after new editions of the SI Brochure have been published (1991 and 1998 at least). Congress delegated to the Secretary of Commerce its power to fix the system of weights and measures, and NIST prepares these documents for his signature.

    It may be of interest to British readers that 2000 and 2003 editions of the MUTCD (Manual for Uniform Traffic Control Devices, our equivalent to TSRGD) authorized and contained examples of metric road signage as well as Customary. Unfortunately, since no State would use it, FHWA removed the metric from the main body of the document and put it in a simplified (and useless?) appendix in the 2009 edition. Nothing says metric road signage is no longer legal, but it would be hard to be sure you are designing it properly without the clear examples and specifications in the prior editions.


  3. The one final step in the UK that is directly under government control, namely road signs, is an absurd omission when they claim to be a (in the words of John Major) “metric country”.
    Whatever the perceived progress toward metrication in the UK compared to the US, dual measures are considered to be normal and the muddle is not important enough to be properly resolved.
    To me the apathy and ignorance is astounding!


  4. A member of the US Metric Association has written to me as follows:

    “Old-timers will remember that several decades ago there was yet another push for metrication. At that time, the Society of Automotive Engineers (SAE), among others, switched to publishing its flagship Automotive Engineering magazine in metric units. I am purposely not saying SI, because old metric units were still there, the editors not knowing better. A decade later, it was back to inch-pound (IP) units at SAE, enacted on protesting “letters from members.” (It was 6 or 8 letters we were told and none of us on the committee saw any of them; the rumor was that they originated with influential retirees).

    Now I am pleased to share with you that, in the latest issue, although still “dual united” here and there, almost all units were SI metric including the most ignored unit of them all, the joule.

    Here are some examples:
    Referring to the Le Mans racing technology the article says “10 MJ per lap” (followed by the silly conversion of (2.77 kWh)). Porsche has 8 MJ assist, Audi 6 MJ (no I-Ps). Car dimensions 4650 mm l., 1050 mm w., 1050 h. (with inches in brackets), but both the displacement volume and fuel capacity in L only.

    Perhaps the new era of fuel efficiency in racing and the existence of both IC and electric cars will accomplish what our generation has not.”

    Is there a UK equivalent of the SAE, and if so how metric is its journal? Can readers advise?


  5. Looks like video gaming might be helping reset the American mindset to accept metric among the younger generation:


    From the About section of Blast:

    What is Blast?

    Blast is journalism for the video game generation. Yes, we cover video games with our reviews, previews, breaking news, interviews, and feature pieces. But Blast Magazine is not just a gaming website. We are an online magazine for Gen-Y, with movie reviews, musician profiles, and long-form magazine features about every topic from drug use and sex to the changing role of the piano and a 24-year-old mortician.”

    Younger Americans are almost certainly more open to metric than older folks and this will just continue the trajectory of the youngsters towards more and more comfort with metric.

    I believe our day is coming here in the USA. At that point you can kiss Imperial good-bye in the UK. (After all, what would be the point for the UK to keep it when the largest economy and the last “Imperial” holdout has converted?)


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