Chain Conversion Chart

The international nautical mile was defined by the First International Extraordinary Hydrographic Conference, Monaco in 1929. This is the only definition in widespread current use, and is the one accepted by the International Bureau of Weights and Measures. Before 1929 different countries had different definitions, and the Soviet Union, the United Kingdom and the United States did not immediately accept the international value.

These measures were abandoned in favor of the international nautical measures in 1954.

These measures were abandoned in favor of the international nautical measures in 1970.

These units are still actively used in some countries of Latin America. Their values vary from country to country. You can find more old Spanish customary units on our historical lengths page.

A rack unit, U or RU is a unit of measure that describes the height of equipment designed to mount in a 19-inch rack or a 23-inch rack. The 19-inch (482.6 mm) or 23-inch (584.2 mm) dimension refers to the width of the equipment mounting frame in the rack including the frame; the width of the equipment that can be mounted inside the rack is less.