# US Customary System Conversions

Two systems of weights and measures are derived from English Units: the US Customary System and the British Imperial System. Neither is dominant worldwide, but they do retain significant usage. For commercial and everyday use, the US Customary System is used in the United States, and the Imperial System still applies to volume and vehicle speed in the United Kingdom.

Therefore, it is important to understand US Customary and Imperial units and their conversions to metric. In fact, there have been some substantial errors in the past associated with unit-based misunderstandings. Most notably, in 1999, due to a mishap with one engineering team using English units while another used SI units, a \$125 million Mars orbiter was lost to the great expanse of space.

English units and their International System of Units (SI) equivalents are listed below. Please note that the National Institute of Standards and Technology (NIST) produces Weights and Measures Publications for areas of legal metrology, laws, regulations, measurement devices, and specifications and tolerances. Much of this information was derived from NIST’s website, as well as some other sources on US Customary Units.

### Mass (Weight)

While these three remain the common units of weight under the Imperial and US Customary Systems, there are actually three systems of weight in English units. The common weight/mass units, as listed above, actually are part of the avoirdupois system, and there is also troy and apothecaries’ weight.

#### Volume

Volume is one of the primary areas in which the US Customary and British Imperial Systems differ. Imperial units for volume are listed below.

### Temperature

Temperature can be converted from Fahrenheit to Celsius, and vice versa, by following the two equations below:

T(°C) = (T(°F) – 32) × 5/9

T(°F) = T(°C) × 9/5 + 32

### Other US Customary Units

Did we miss anything? Are there any other units you’d like to add to this list? Comment below, and we’ll add anything accordingly.

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## US Customary System

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