Why Does the US Still Use Imperial Measurements? The Full Story

The United States, Liberia, and Myanmar are the only three countries that have not adopted the metric system as their primary measurement standard. For a country that prides itself on innovation and efficiency, the continued use of miles, Fahrenheit, and fluid ounces can seem puzzling. The explanation involves a failed Congressional act, a shipwreck, a war, and a deeply embedded cultural resistance to change.

The US Was Almost Metric in the 1790s

The story begins right after American independence. Thomas Jefferson, as Secretary of State, was tasked with standardising US weights and measures. He proposed a decimal-based system in 1790 — strikingly similar to what the French were developing simultaneously. Congress considered it seriously but ultimately chose to keep the familiar British units that colonists already used.

France sent a representative, Joseph Dombey, to Washington with a copper cylinder representing the new metric kilogram. His ship was blown off course by a storm and captured by pirates near Guadeloupe. Dombey died in captivity. The kilogram cylinder was sold at auction. Whether or not this changed history is debatable — but America and metric had a famously bad first meeting.

The Metric Conversion Act of 1975

After the metric system became mandatory for international trade and science throughout the 20th century, the US made its most serious attempt at conversion. The Metric Conversion Act of 1975 declared the metric system the preferred system of weights and measures for United States trade and commerce — and established the US Metric Board to coordinate the transition.

The conversion was voluntary. Without mandates or deadlines, industry had no obligation to switch. Public resistance was fierce: petitions, letters to Congress, protests. Americans saw metric as foreign, confusing, and unnecessary. The Carter administration supported it; the Reagan administration abolished the Metric Board in 1982, citing budget cuts. The voluntary transition quietly died.

Where the US Already Uses Metric

The picture is less black-and-white than most people realise. Metric is deeply embedded in American life in specific domains:

• Medicine and pharmacy — all drug dosages in the US are in milligrams, millilitres, and micrograms
• Science and research — all US scientific work uses SI units exclusively
• Military — the US Armed Forces use metric for most equipment and logistics
• Nutrition labels — since 1994, US food labels show grams, milligrams, and calories (a metric unit)
• Photography and film — lens focal lengths, sensor sizes in millimetres
• Automotive — engine displacement in litres (a 5.0L Mustang), torque in newton-metres for engineering specs
• Soft drinks — sold in 2-litre bottles since the 1970s
• Track and field — 100m, 400m, marathon (42.195 km)

The Real Cost of Not Going Metric

Staying imperial has a measurable price. US manufacturers producing for global export must maintain dual measurement systems, increasing design complexity and manufacturing cost. The famous Mars Climate Orbiter failure in 1999 — caused by a metric/imperial unit mismatch — cost $327 million. Engineering and construction firms operating internationally routinely cite conversion errors as a source of expensive mistakes.

A 1992 study estimated that the US economy loses billions of dollars annually through inefficiencies caused by dual systems in international trade, manufacturing, and engineering. Yet the political will to change has never materialised.

Why Change Has Not Happened

Economists and historians point to several compounding reasons. First, the sheer scale of the US internal market means that most American businesses can operate entirely within the country without ever needing metric. Second, the infrastructure investment required — road signs, speedometers, building codes, textbooks — runs into hundreds of billions of dollars. Third, and perhaps most powerfully, Americans have simply never felt the daily friction that makes metric feel necessary.

Countries that successfully converted — Australia in 1974, Canada in the 1970s–80s, the UK gradually throughout the 1960s–2000s — typically did so with government mandates, education campaigns, and coordinated industry transitions. The US has never had all three at once.

Will the US Ever Go Metric?

De facto metrication is already happening. Younger Americans, educated in schools that teach both systems, are increasingly comfortable with metric. Global brands, international supply chains, and digital tools that convert instantly are reducing the friction. Many experts believe the US will arrive at metric gradually and informally — not through a dramatic conversion act, but through the slow disappearance of imperial units from contexts where they no longer serve anyone well.

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