What Countries Use the Customary System?
As of 2014, the United States, Liberia and Myanmar are the only three countries that still use the customary system of measurement instead of the metric system. This system, based on the old British Imperial System, is a hodgepodge of different measurement standards that are often hard to reconcile.
Congress chose the American customary system as the national standard early in the country's development, as they are empowered to by Article 1, Section 8 of the Constitution. Thomas Jefferson wanted to use the new French metric system, but was reluctant at that point in history to invest in the necessary trip to France to acquire accurate measurements. Soon afterward, relations between France and the United States cooled, and it was determined that the American customary system was adequately uniform anyway. In the 1860s, the European-standard metric system was adopted as an alternate measurement system, but the American customary system remains the official standard.
Liberia, a country founded by the United States as a home for freed slaves, and the Southeast Asian country Myanmar also still use the customary system. However, recently both have been moving toward making the metric system the official legal standard. Despite its official status throughout the world, the customary system is still in everyday use in many countries, including Great Britain and much of northern Europe.