# Metric system

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The metric system is an international decimalised system of measurement, first adopted by France in 1791, that is the common system of measuring units used by most of the world. It exists in several variations, with different choices of fundamental units, though the choice of base units does not affect its day-to-day use. Over the last two centuries, different variants have been considered the metric system. Since the 1960s the International System of Units ("Système international d'unités" in French, hence "SI") has been the internationally recognised standard metric system. Metric units are universally used in scientific work, and widely used around the world for personal and commercial purposes. A standard set of prefixes in powers of ten may be used to derive larger and smaller units from the base units.

The International System of Units is the official system of measurement for all nations in the world except for Burma, Liberia, and the United States.[1] (Some sources identify Burma or Liberia as metric, however.[2]) However, a number of other jurisdictions have laws mandating or permitting other systems of measurement in some or all contexts, such as the United Kingdom – where for example the Traffic Sign Regulations (TSRGD) only allow distance signs displaying imperial units (miles or yards)[3] – or Hong Kong.[4] In the United States, metric units are widely used in science, military, and partially in industry, but customary units predominate in household use. At retail stores, the litre is a commonly used unit for volume, especially on bottles of beverages, and milligrams are used to denominate the amounts of medications, rather than grains. Also, other standardised measuring systems other than metric are still in universal international use, such as nautical miles and knots in international aviation.