Why Does the US Still Use Imperial Units?

The United States is one of only three countries in the world — alongside Myanmar and Liberia — that has not officially adopted the metric system as its primary measurement standard. Given that the US helped define the modern world, this is a striking exception. How did it happen?

The US Almost Switched in 1975

The Metric Conversion Act of 1975 established a national policy of voluntarily converting to the metric system. A Metric Board was created to coordinate the transition. But 'voluntary' meant optional — and most businesses and consumers chose not to change. Ronald Reagan disbanded the Metric Board in 1982, effectively ending the effort.

Infrastructure Lock-In

Switching measurement systems isn't just about education. It means replacing road signs, retooling manufacturing equipment, reprinting every manual, and retaining an entire workforce. The cost estimates for a full US conversion run into hundreds of billions of dollars. The short-term disruption has always outweighed the long-term benefits in political calculations.

Where the US Already Uses Metric

Metric is actually everywhere in American life — most people just don't notice. All pharmaceuticals are dosed in milligrams. Nutrition labels list grams. Wine and spirits are sold in 750 mL bottles. Science and engineering use metric almost exclusively. The US military uses metric for equipment interoperability with NATO allies.

Real Costs of the Dual System

Maintaining two systems creates real risks. The 1999 Mars Climate Orbiter crash — caused by a team using pound-force seconds instead of newton-seconds — cost $125 million. Medical dosing errors caused by unit confusion are a documented safety risk. Trade with metric-using countries requires constant conversion and adds friction to international commerce.