Which Nations Officially Adopt the Imperial System?

Globally, the metric system dominates daily measurements — at medical appointments, height is measured in centimeters and weight in kilograms, while recipes specify ingredients in grams and milliliters.

While the United States stands out as a major exception, are there other countries that follow suit? Which nations utilize the imperial system?

Which Nations Officially Utilize the Imperial System?

Globally, only three nations officially employ the imperial system for measurements: the United States, Liberia, and Myanmar [source: Buchholz].

Certain countries, such as Canada, have adopted the metric system as their official standard but permit the imperial system in various applications [Source: McQuillan]. In 2021, the UK government revealed intentions to revert to the imperial system following its departure from the European Union [source: Gross].

Nevertheless, every nation has either fully embraced or legally recognized the International System of Units (SI), the contemporary version of the metric system. This includes the U.S., Liberia, and Myanmar.

Current Measurement Practices in the United States

Measurement practices in the United States remain inconsistent and complex:

These are merely a handful of instances. The U.S. Customary System, also known as the inch-pound system, encompasses over 300 distinct units for measuring different physical quantities. Many of these units share the same name but carry vastly different definitions.

On the U.S. Metric Association website, Dennis Brownridge highlights at least nine interpretations of the unit referred to as a "ton": short ton, displacement ton, refrigeration ton, nuclear ton, freight ton, register ton, metric ton, assay ton, and ton of coal equivalent.

The Evolution of the Metric System in the United States

As part of the British Empire, North American colonists adopted and utilized the British Imperial System, which originated from a complex web of medieval measurements. Even as France refined the metric system in the late 18th century, England and its colonies continued to rely on an outdated measurement framework.

Colonial leaders were not indifferent to the need for standardization. The U.S. Constitution, in Article I, Section 8, granted Congress the authority "to coin Money ... and establish the Standard of Weights and Measures."

In 1790, Thomas Jefferson, serving as George Washington's Secretary of State, was tasked with addressing this mandate. Jefferson favored a decimal-based measurement system but hesitated to adopt the metric system. He was concerned about the impracticality of verifying the metric unit of length without sending an expensive delegation to France.

The political climate further complicated the rivalry between the imperial and metric systems. Despite France's support during the Revolutionary War, relations soured after the ratification of Jay's Treaty in 1795.

The French perceived the treaty, which removed British influence from the Northwest Territories and granted the U.S. limited trade rights in the West Indies, as evidence of a growing alliance between America and England.

In retaliation, France deployed privateers to attack American merchant vessels. By 1797, when John Adams assumed the presidency, tensions between the U.S. and France had escalated significantly. Consequently, it was unsurprising that in 1798, France excluded the U.S. from its invitation to foreign dignitaries to visit Paris and learn about the metric system.

Even if U.S. delegates had attended the 1798 Paris event and been impressed by the metric system, it is doubtful they could have convinced American leaders to overhaul the nation's measurement standards.

In 1821, Secretary of State John Quincy Adams reviewed the measurement units used across the 22 states and concluded that the U.S. Customary System was adequately consistent and needed no modifications. Additionally, American politicians were wary that France's dedication to the metric system might waver following Napoleon Bonaparte's tumultuous reign in the early 19th century.

The U.S. Move to Acknowledge the Metric System

Gradually, the metric system gained widespread acceptance. By the conclusion of the American Civil War in 1865, much of Europe had embraced the decimal-based system, leaving the U.S. with no choice but to take notice.

In 1866, President Andrew Johnson signed a congressional act into law, permitting the use of metric weights and measures "throughout the United States in all contracts, transactions, or legal proceedings."

When France convened global leaders to discuss a modernized international metric system, the U.S. was invited and sent representatives. The participating nations signed the Treaty of the Meter, creating the International Bureau of Weights and Measures, an overseeing committee, and a General Conference to review and implement updates.

The treaty also mandated the establishment of a laboratory in Sèvres, near Paris, to store international metric standards like the International Prototype Metre and facilitate their distribution to ratifying countries.

In 1890, the U.S. received replicas of the International Prototype Metre and Kilogram. The Mendenhall Order of 1893, named after T.C. Mendenhall, then Superintendent of Weights and Measures, mandated that U.S. standards for length and mass align with metric units. The yard was defined as 3600/3937 of a meter, and the pound-mass as 0.4535924277 kilogram.

In 1959, English-speaking nations reached a consensus on updated conversion standards: 1 yard was defined as exactly 0.9144 meters, and 1 pound-mass as precisely 0.45359237 kilograms.

This signifies that the U.S. has formally and legally acknowledged the metric system for more than 150 years, with its standard weights and measures rooted in metric units for over 120 years. However, formal recognition does not always equate to widespread adoption.

The Current State of the Metric System in the U.S.

Mendenhall was among the increasing number of scientists and policymakers pushing for mandatory use of the metric system in the U.S. However, by the time of his death in 1924, the nation had yet to make the transition.

Change appeared imminent in 1971 when a U.S. National Bureau of Standards report, "A Metric America," proposed a 10-year plan for the U.S. to adopt the metric system. In 1975, Congress passed the Metric Conversion Act but removed the 10-year deadline, making the shift voluntary.

Despite American students diligently learning SI units and some companies adopting metric measurements, the push for nationwide metrication lost momentum, and efforts to transition largely stalled.

Economic Implications of Metric and Imperial Systems

As globalization expanded, U.S. businesses increasingly competed on an international stage. Foreign clients purchasing American products often demanded that they be manufactured, labeled, and shipped using metric units.

When American firms established new facilities in Europe or Asia, they confronted the dilemma of adhering to U.S. measurements or adopting the metric system — choices with significant financial implications.

Acknowledging these challenges, Congress amended the Metric Conversion Act in 1988, declaring the metric system as the "preferred system of weights and measures for U.S. trade and commerce" and mandating federal agencies to adopt "the metric system in procurement, grants, and other business operations" by the end of 1992.

The amendments maintained voluntary metrication for private businesses, and while they promoted federal support for small enterprises transitioning to metric, progress has been sluggish.

Hard Metric Versus Soft Metric

Approximately 30 percent of products made by U.S. companies have adopted metric measurements [source: Smith]. The pharmaceutical industry has fully embraced "hard metric," displaying only metric units. In contrast, beverages often feature both U.S. Customary and metric units, classifying them as "soft metric." Products like film, tools, and bicycles are also marketed using metric measurements.

Despite these changes, the U.S. remains the sole industrialized country that has not mandated the metric system.

Transitioning to Meters Comes at a Cost

One major barrier to the U.S. adopting the metric system is the expense. Updating technical diagrams and manuals for intricate machinery with numerous components can consume thousands of hours.

For instance, NASA engineers estimated that transitioning the space shuttle's relevant documents, software, and designs to SI units would cost $370 million — roughly half the price of a standard shuttle launch [source: Marks].

However, cost isn't the sole factor behind the U.S.'s hesitation. Psychological factors also contribute significantly; individualism is deeply ingrained in American culture. One could imagine bumper stickers echoing the National Rifle Association's (NRA) famous phrase: "You'll get my inch-pounds only when you take them from my cold, dead hands."

The most plausible explanation, though, may be Congress's failure to mandate the metric system across all 50 states, the District of Columbia, and U.S. territories. By keeping conversion optional in all major laws since 1866, the U.S. has allowed traditional units to persist in everyday transactions affecting ordinary citizens.