The metric system, now known as the International System of Units (SI), is an internationally recognized, decimalized system of measure. The metric system uses the meter, liter, and gram as units of length, capacity, and weight or mass. Its base units are meter for length, kilogram for mass, second for time, ampere for electrical current, kelvin for temperature, candela for luminous intensity, and mole for quantity.
All metric units are derived from the meter. A gram is one cubic centimeter of water at its maximum density and a liter is 1/1000 of a cubic meter. Greek prefixes are used to distinguish multiples of 10: deca (10), hecto (100), myria (10,000), kilo (1,000), and so on. Latin prefixes are used for the submultiples (amounts less than 1): deci (0.1), centi (0.01), milli (0.001), and so on.
The metric system was born in France after the French Revolution in 1789. The French National Assembly directed the French Academy of Sciences to address and fix the system of French weights and measures, which decided to base the system on a natural physical unit. The Academy decided on the length of 1/10,000,000 (one ten-millionth) of a quadrant of a great circle of the earth. The meter is the result of a six-year survey that eventually yielded a value of 39,37008 inches.
The metric system gained traction rapidly between 1850 and 1900. The French decided to turn the system over to international control, and in 1875, an International Bureau of Weights and Measures met in Paris to sign the Treaty of the Meter. Forty countries, including the United States but excluding Britain, signed the treaty, establishing the International Bureau of Weights and Measures. The metric system met general opposition in every country at the time of its adoption, which has been overcome everywhere except for the United States.
Three countries in the world do not use the metric system as the official system of measurement: the United States, Liberia, and Myanmar.
The United States’ reluctance to fully adopt the metric system stems from when the British colonized the New World, bringing the Imperial System with them. After independence, secretary of state Thomas Jefferson insisted on using the imperial measurement system despite Congress proposing to use the metric system. The metric system is used in the United States, but it is not the official system of measurement.
Liberia was founded by the American Colonization Society; therefore, Liberia’s laws were founded based on the American Constitution. Because of the country’s close association with the United States, Liberia still uses the imperial measurement system. The government, however, is in the process of adopting the metric system.
Myanmar isolated itself after gaining independence from Britain; therefore, it never required a common measurement system with the rest of the world. After using its own traditional forms of measurements, Myanmar is in the process of adopting the metric system now that it is open to the rest of the world.
It is likely that the United States will soon be the only country in the world that has not fully adopted the metric system.