An “Island in a Metric Sea”: America and the Metric System

¹In late 1975, President Gerald Ford had a unique vision for making America great again. He wanted to embrace a French invention – one that Thomas Jefferson himself had championed. He wanted America to go metric. He signed the Metric Conversion Act of 1975 into law.

“To say that this legislation is historic,” Ford proclaimed, “[was] an understatement.”² For too long, he explained, America had been dependent upon “the English system of measurement”³ – of feet, inches, pounds, ounces and miles. Yet, he said, “more than 90 percent of the world’s people” used metric measurement in their “everyday lives,” putting America out of step with overseas markets. The result, he lamented, was that the United States was “an island in a metric sea.”⁴

The Metric Conversion Act, Ford predicted, would correct the problem. It created a “Metric Conversion Board,” to enable the United States to convert to the International System of Units, or “SI,” a.k.a. the metric system, by 1992.⁵ Kilometers, grams and hectares, as well as Celsius temperature, would be the measure of all things.

1992 came and went, and metrication never happened. The public, and indeed U.S. policymakers, abandoned the idea at virtually the first hurdle. The standard system seems to be a permanent fixture of American life.

Yet metric has penetrated further than most people realize. Not only is metric now used in many facets of American life, such as the U.S. military (e.g. the Army’s use of kilometers, or “clicks,” for measurement), science and medicine, but every American also has a statutory right to use the metric system in place of the standard system. The United States is also a founding member of the 1875 Metric Convention, and thus participates in the international body that presides over the metric system. Perhaps more fundamentally, American standard measurements have been pegged to metric for over a century, so that recent changes to the metric system (e.g. in the way a kilogram is measured) have a direct impact on the American standard system. Indeed, in a real sense, one can question whether standard measurements exist at all.

1. America’s Founders Call for a Standard System of Weights and Measures

The framers of the United States Constitution, as adopted in 1787, empowered Congress to “fix the Standard of Weights and Measures.”⁶ It seemed natural to expect that Congress would soon do this, given the shortcomings in traditional English measurements. Among other things, they were non-decimal (with twelve inches to a foot, three feet to a yard, for example) and contained units (e.g. yards and miles) that did not correlate with each other.

Congress seemed headed toward reform when it enacted the Coinage Act of 1792, which decimalized currency (thus giving us dollars and cents). And in the same decade, the French Revolution produced a seemingly ideal alterative – and decimalized – model, in the form of the new metric system.

2. America’s “Standard” System Sticks with British Measurements

The metric system, as launched in 1799, was a complete break with the past: it expressed mass (or weight) in grams and kilograms, and distance in metres (or meters, in American English). Since it was now decimalized, fractions of a unit (e.g. a meter) could be expressed using decimal places (or via sub-units such as centimeters or millimeters), and large distances could be expressed in the hundreds or thousands (e.g. a kilometer is 1000 meters). Together with these measurements, French scientists created “fundamental” prototypes to represent the kilogram and meter.

Despite winning adherents within the United States (e.g. Thomas Jefferson, predictably, favored its adoption),⁷ and despite quickly spreading throughout continental Europe, the metric system did not take off in North America. Instead, the United States continued with the traditional English system of yards, feet and pounds.

The English system itself was subject to a general upgrade in 1824, when the United Kingdom passed legislation rebranding it as the “Imperial” system and extending it to the whole of Great Britain and its Empire (then including India and the countries of the present-day Commonwealth). The legislation was backed up with (literal) yardsticks – such as the “Imperial Standard Yard,” a straight brass rod held at the House of Commons in Westminster,⁸ and the “Imperial Standard Troy Pound” (a brass prototype also held at Westminster).⁹

The United States government effectively embraced this revamped system (while conveniently re-labeled as the “standard” system). In 1828, Congress passed a law “to continue the Mint at the City of Philadelphia” that provided that, “for the purpose of securing a due conformity in weight of the coins of the United States,” the U.S. mint was to utilize “the brass troy pound weight procured by the minister of the United States at London.”¹⁰ In the 1830s, the U.S. Treasury began publishing standard systems for weights and measurements – and, for these purposes, obtained exact copies of the UK Imperial yard and pound prototypes.¹¹

In 1836, the U.S. Treasury formed the U.S. Office of Standard Weights and Measures, in 1901, this became the National Bureau of Standards, and in 1903 it became the Bureau of Standards under a new U.S. Department of Commerce and Labor. In 1988, the National Institute of Standards and Technology (“NIST”). By statute, it is charged with “develop[ing], maintain[ing] and retain[ing] custody of the national standards of measurement and provid[ing] the means and methods for making measurements consistent with those standards.”¹²

3. 1866 Onward: The United States Becomes Metric-Friendly

In 1866, the U.S. Congress took a small step toward adopting the metric system through the “Metric Act.” This statute provided that it was “lawful” to employ metric weights and measures within the United States, and further stated that “no contract or dealing, or pleading in any court, shall be deemed invalid or liable to objection” because of the use of the metric system.¹³

In 1875, the United States went further: it became a founding member of the Metric Convention (or Treaty of the Meter). Under this Convention, the “General Convention on Weights and Measures” (a standing organization that periodically meets in Paris) is the ultimate governing body for the metric system – or System International/SI.¹⁴ The Bureau International des Poids et Mesures (“BIPM”), also based in Paris and reporting to the General Convention, is metric’s regulator.

One of the first tasks for the BIPM was to establish new, scientifically robust, metric prototypes. Thus:

• in 1879, the BIPM created “Le Grand K” (“The Big K”), a gold-ball sized cylinder comprised of platinum and iridium, whose mass was deemed to be exactly one kilogram. It was “[k]ept in a triple-locked vault on the outskirts of Paris”;¹⁵ and
• In 1889, the BIPM endorsed a prototype “meter”: a platinum-iridium bar, also held in BIPM’s Paris vault – with two lines one exact meter apart.¹⁶

The United States, as a member of the Meter Convention, was entitled to receive copies of these prototypes, and when they arrived in 1890, their “packing cases” were “opened at the White House and accepted by President Harrison.”¹⁷ Their impact was profound. Indeed, only a few years later, the United States government abandoned reliance on UK “imperial” prototypes altogether.

4. The Mendenhall Order — American Standard
   Measurements Are Pegged to the Metric System

In 1893, the U.S. government issued the “Mendenhall Order,” directing that American weights and measures would henceforth be pegged to the metric system.¹⁸ This system, with some modifications, continues to apply today. Thus:

• An American standard pound is equal to 0.45359237 kilograms.¹⁹
• An American yard is 0.9144 meters.²⁰ By extension, the same pegging applies to inches and miles.²¹
• Volume in the metric system is measured by the liter, defined as one cubic decimeter (i.e. it is derivative of the meter).²² It follows that the U.S. gallon (defined by the NIST as 231 cubic inches)²³ is also ultimately tied to the metric meter.

In 1921, the Metric Convention was amended so that the SI/metric system embraces other physical measurements. Thus, for example:

• Temperature. The base unit of temperature is the kelvin. Zero Kelvin (equal to -273.150° C or -459.670°F) is the point of “absolute” or “infinite” cold, i.e., the point where the laws of physics do not permit one to be any colder.²⁴ This in turn serves as the reckoning point for both Celsius²⁵ and Fahrenheit.²⁶
• Time. The base unit of time– the second – was brought into the SI/metric system and standardized by the General Convention in 1967 using “an atomic standard of time, based on a transition between two energy levels of an atom or a molecule.”²⁷ It adopted a definition of the second “referenced to the frequency of the ground state hyperfine transition in the cesium-133 atom.”²⁸
• Physics measurements (e.g. Newton, as the unit of force) and electrical measurements (the amp, watt, volt, etc.) are all part of the broader SI/metric system. Included in the SI/metric system’s physical measurements is the joule (the unit of heat, energy and work) – defined as the amount of “work required to move a distance of one meter against a force of one newton.”²⁹ In the American standard system, a calorie is pegged at 4.184 joules, although it is also defined as “[t]he amount of heat necessary to raise 1 gram of water 1C at the pressure of 1 atmosphere and temperature of 15C.”³⁰

The pegging of the standard system to the metric system is in line with the scientific community’s broader embrace of the metric system – which finds parallels in the adoption of metric by the U.S. military, in medicine and pharmaceutical industries, and in many sports. It also reflects the increasingly broad acceptance of the metric system, even in countries that previously used Imperial measurements. Thus, despite the failure of official metrication in the 1970s, metric plays a large role in U.S. life.

Importantly also, the metric system’s definitions are not static. In 1983, for example the General Conference abandoned the 1879 prototype meter in favor of a more scientific method of measuring distance. A meter was re defined as “the length of the path traveled by light in a vacuum [during a time interval with duration] of 1/299 792 458 of a second.”³¹

In all these matters, the United States, through its members of the Metric Convention, plays a critical (and at times leading) role, as witnessed by the most recent set of redefinitions.

5. The 2019 Reforms Conform all Measurements
   (Metric and Standard) to Scientific Constants

In 2019 the General Convention on Weights and Measures enacted some of its most ambitious reforms to date, all intended to make the SI/metric system a universal objective system based on scientific constants.

Mass/weight. Effective 2019, the venerable “Grand K” was retired after more than a century of service, in favor of a formula that draws on quantum mechanics. A kilogram is now derived by reference to the “Planck constant,” a mathematical constant that is tied to the fundamental properties of all matter.³² In theory, this means that the kilogram can be generated anywhere in the universe, or at least anywhere where scientists can build a “Kibble balance, a complex device that measures mass precisely through the use of electrical measurements.”³³

Time. The 2019 reforms also refine the measurement of the second. It is still governed by atomic clock principles (and the properties of the cesium atom), but was slightly tweaked in 2019, to be “equal to the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the unperturbed ground state of the ¹³³Cs atom.”³⁴

Temperature. Until 2019, a kelvin was determined by taking the “triple point of water” (to laypeople, freezing point), and then assigning it the value of 273.16 K.³⁵ From 2019, the kelvin is now measured by reference to the “Boltzmann constant,” a scientific number representing the “average energy content of a gas.”³⁶

Although these 2019 changes went largely unheralded at the time, they were done with the full participation of the NIST (and in some cases spearheaded by its scientists). And because the United States standard measurement system is pegged to metric, the 2019 reforms now have altered the fundamental measurement of weights (pounds, ounces and tons), as well as the Fahrenheit temperature scale.

* * *

The American public has proved stubbornly fond of its “yards” and “pounds.” Yet few realize that the “standard” American measures system is now entirely derivative of the metric system/SI — which means that the metric system now underpins literally every ounce and inch, as well as every calorie we try to burn. President Ford’s vision of a metric America might not yet have materialized, but it is no longer an island in a metric sea.

The opinions expressed in this article are those of the authors and do not necessarily reflect the views of Skadden or its clients.

1. B.A. L.L.B. (University of New South Wales), B.C.L. (University of Oxford). Mr. Nelson is a Partner in the International Litigation and Arbitration Group of Skadden, Arps, Slate, Meagher & Flom LLP, New York. Copyright 2025 by the author. The views expressed herein are solely those of the author and are not necessarily those of Skadden Arps or any one or more of its clients.
2. Gerald R. Ford, “Statement on Signing the Metric Conversion Act of 1975” (Dec. 23, 1975).
3. Id.
4. Id.
5. See 15 U.S.C. § 205b; see also id. § 205d.
6. U.S. Const., art. I, s. 8, cl. 5.
7. Keith Martin, Pirates of the Caribbean (Metric Edition) (2017), available at https://www.nist.gov/blogs/taking-measure/pirates-caribbean-metric-edition.
8. Weights & Measures Act 1824 § 1 (U.K.).
9. Id. § 4.
10. 4 Stat. 277, 278 (1828); see also Louis A. Fischer, History of the Standard Weights & Measures of the United States, 1 Bulletin of the Bureau of Standards 365, 369-70 (1905). The British prototypes needed to be replaced after the House of Commons was burned down in 1834, but the British authorities cooperated in supplying replacement copy prototypes to the United States. T.C. Mendenhall, “The United States Fundamental Standards of Length and Mass,” 56 Science 377, 378-79 (1922)
11. Fischer, supra note 9, at 372.
12. 15 U.S.C. § 272(b)(2).
13. 15 U.S.C. § 204; see also 15 U.S.C. § 205 (permitting the use of grams, liters, meters and their various multiples or sub-multiples in contracts and pleadings throughout the United States).
14. https://www.bipm.org/en/metre-convention
15. https://www.nist.gov/si-redefinition/kilogram
16. See https://www.bipm.org/en/history-si/metre
17. Lewis Judson, Weights and Measures Standards of the United States: A Brief History in U.S. Dept of Commerce National Bureau of Standards Miscellaneous Publication 247 (1963).
18. Mendenhall, supra note 9, at 377. The bureaucrat and scientist who issued it, Thomas Corwin Mendenhall, was then Superintendent of the U.S. Coast and Geodetic Survey.
19. National Bureau of Standards, Refinement of Values for the Yard and Pound (June 25, 1959), available at https://www.ngs.noaa.gov/PUBS_LIB/FedRegister/FRdoc59-5442.pdf
20. Id.
21. See Customary Systems of Weights and Measures (July 26, 1968) in Weights and Measures Standards of the United States: a brief history, NBS Special Publication 447, Appendix 8 (“5,280 feet = l statute mile = 1.609 kilometers”; “12 inches = l foot = 0.3048 meter”), available at https://www.govinfo.gov/content/pkg/GOVPUB-C13-691a9b38e29a85d0925f4db586b60735/pdf/GOVPUB-C13-691a9b38e29a85d0925f4db586b60735.pdf
22. https://www.nist.gov/pml/owm/si-units-volume.
23. See https://www.nist.gov/system/files/documents/pml/wmd/pubs/2016/02/18/appc-16-hb44-final.pdf
24. https://www.nist.gov/si-redefinition/kelvin-introduction
25. Celsius and Kelvin are calibrated the same; the difference between the systems only being the starting point 0° Celsius is the freezing temperature of water. Id.
26. Under the NIST conversion chart, a Fahrenheit temperature can be obtained using the formula (K - 273.15) * 1.8 + 32, where K is the temperature in Kelvins. Id.
27. See “Historical Perspective: Unit of time, second,” available at https://www.bipm.org/en/history-si/second.
28. Id.
29. https://www.nist.gov/glossary-term/26261#:~:text=A%20joule%20is%20the%20heat,watt%20is%20a%20joule%2Fsecond
30. https://www.nist.gov/glossary-term/19621
31. See NIST has measured the speed of light in various ways, including using lasers to interact with methane gas, as well as “modulating the light from the 633 nm line of a helium-neon laser using microwaves.” See https://www.nist.gov/si-redefinition/meter. In each case, the speed of light in a vacuum (“c”) came to within 299,792,456 and 299,792,462 meters per second. Id. The SI definition of the meter fixes the speed of light in a vacuum as being 299,792,458 meters per second. https://www.bipm.org/en/measurement-units/.
32. “The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be 6.626 070 15 x 10–34 when expressed in the unit J s, which is equal to kg m2 s–1.” https://www.bipm.org/metrology/mass/units.html.
33. https://www.nist.gov/si-redefinition/kilogram-introduction
34. Definition agreed by the 26th CGPM (Nov. 2018), implemented May 20, 2019, available at https://www.bipm.org/en/si-base-units/second
35. https://www.nist.gov/si-redefinition/kelvin-introduction
36. See https://www.nist.gov/si-redefinition/kelvin-boltzmann-constant; see also https://www.bipm.org/en/si-base-units/kelvin (under the 2019 redefinition, “one kelvin is equal to the change of thermodynamic temperature that results in a change of thermal energy k T by 1.380 649 x 10^–23”).