You may have heard that only three countries do not use metric: the United States, Liberia and Myanmar. In a 2020 blog post, the US National Institute of Standards and Technology, or NIST, calls that claim “simply untrue”. Here is what it says.
What the metric system is
The metric system’s formal name is the International System of Units (SI). NIST says every country has accepted the SI, the United States included. Some countries make metric mandatory, while in others it is optional.
Why the claim is wrong
NIST points to Russ Rowlett, a retired university professor. In his view, a country does not switch to metric on one day. It moves toward metric step by step. Every economy, he says, sits somewhere along a “continuum” of metric use. NIST adds that some measures in the US are entirely metric. A country is not simply “metric” or “not metric”.
The United States uses metric every day
NIST lists several facts.
- Metric has been legal in the US since 1866.
- In 1875, the US was one of the first countries to join the Treaty of the Meter.
- President Gerald Ford signed the Metric Conversion Act on 23 December 1975.
- In 1988, metric became the preferred system for US trade and commerce.
- Since 1893, the US has defined mass, length and volume using metric units. NIST adds that all customary units, such as feet, pounds and gallons, rest on the SI.
Even the second belongs to the SI. It is the base unit of time. US coins and banknotes are also made to metric specifications.
What “imperial” means
Britannica says imperial units were Britain’s official measures from 1824. Britain began adopting the metric system in 1965. US customary units come from the imperial system. Imperial units today are legally defined in metric terms.
