The inch, foot and yard are U.S. customary units of length derived from the imperial system of measurement, used primarily in the United States. The meter, decimeter, centimeter and millimeter are units of length in the metric system. This system is used in most of the rest of the industrialized world and is favored for its ease of use. The system is based on units of 10, with conversions often involving little more than moving a decimal point to the right or left.
Originally, a meter was intended to be equal to one ten-millionth of the distance from the Earth's equator to the North Pole, but its definition has evolved over time. Like other units of the metric system, meters are easily divisible by powers of ten. Many decimal innovators, including Thomas Jefferson, preferred standardized units to use decimal systems. As of 2014, the only countries that have not adopted the metric system are the United States, Myanmar and Liberia.Learn more about Measurements