Why Does the US Still Use Imperial Measurements?

The United States shares its measurement system with only two other countries: Liberia and Myanmar. While the rest of the world measures distances in kilometers, weights in kilograms, and temperatures in Celsius, Americans use miles, pounds, and Fahrenheit. This isn't stubbornness — it's history.

The British Inheritance

The US adopted British imperial units during the colonial period, long before the metric system was invented. By the time France introduced the meter in the 1790s, American infrastructure, trade, and tooling were already built around inches, feet, yards, and miles.

The irony is that Britain itself went metric in the 1960s and 1970s. The US, once the cultural heir to British measurement, became one of the last holdouts.

The Metric Conversion Act of 1975

The US government has tried to go metric. After the 1973 oil crisis highlighted how out of step American manufacturing was with global standards, Congress passed the Metric Conversion Act in 1975, designating the metric system as the "preferred" system of measurement.

But the act made conversion voluntary. Without a mandate, most industries simply didn't bother. The public was largely indifferent or hostile — metrication meant re-learning everything from scratch, replacing road signs, and retooling factories. The political will wasn't there.

Where Metric Already Won

The US uses metric extensively — just invisibly. All pharmaceutical drugs are measured in milligrams and milliliters. The US military uses metric. Scientists work exclusively in SI units. The soda you buy at a gas station comes in two-liter bottles.

Two-liter bottles, incidentally, were introduced in the 1970s as a metric-friendly packaging size — and Americans adopted them without complaint, never noticing they were using metric.

The Real Cost

The persistence of imperial units has real economic consequences. In 1999, NASA's Mars Climate Orbiter was lost because one engineering team used metric units while another used imperial — a $327 million mistake. International trade requires constant conversion. American-made products often can't be sold abroad without re-engineering them to metric specifications.

Why It Persists

Infrastructure, familiarity, and network effects. Every road sign in the US says miles. Every American knows roughly how tall six feet is or how far a mile run is. Changing that requires not just new signage but a generational shift in intuition.

The transition is also asymmetric: the cost of switching falls on Americans, but the benefits mostly accrue to international trade. For the average person driving to work, there's no reason to care.

Until they travel internationally. Then the unit conversions begin.