Who uses the Metric System? The entire world uses the metric system or The International System of Units (SI) for measurements except for Liberia, Myanmar, and the United States of America. In the USA they use Customary Units like inches, feet, pounds, quarts, and gallons. This is fine except that you have to memorize or look up the strange conversions to get from one unit to another. What is the Metric System? To avoid confusion and strange conversions, scientists around the world have adopted the metric system, which is based on multiples of 10. There are seven base units in the Metric System: the meter (m), the kilogram (kg), the second (s), the kelvin (K), the ampere (A), the mole (mol), and the candela (cd). In order to measure anything smaller or larger than these base units, you can add a prefix that the multiple of 10. There are six prefixes that go smaller and larger than the base unit. Though there are 7 base units, meter, liter, and gram are the ones that you're most l