United States customary units
Consequently, while many U.S. units are essentially similar to their imperial counterparts, there are noticeable differences between the systems.
The majority of U.S. customary units were redefined in terms of the meter and kilogram with the Mendenhall Order of 1893 and, in practice, for many years before.
In science, medicine, many sectors of industry, and some government and military areas, metric units are used.
The customary system was championed by the U.S.-based International Institute for Preserving and Perfecting Weights and Measures in the late 19th century.
The president of an Ohio auxiliary of the Institute wrote that the traditional units were "a just weight and a just measure, which alone are acceptable to the Lord".
The legislation states that the federal government has a responsibility to assist industry as it voluntarily converts to the metric system, i.e., metrification.
[8] Executive Order 12770, signed by President George H. W. Bush on July 25, 1991, citing the Metric Conversion Act, directed departments and agencies within the executive branch of the United States Government to "take all appropriate measures within their authority" to use the metric system "as the preferred system of weights and measures for United States trade and commerce" and authorized the Secretary of Commerce "to charter an Interagency Council on Metric Policy ('ICMP'), which will assist the Secretary in coordinating Federal Government-wide implementation of this order."
Metric units are standard in the fields of science, medicine, and engineering, as well as many sectors of industry and government, including the military.
[8] There are anecdotal objections to the use of metric units in carpentry and the building trades, on the basis that it is easier to remember an integer number of inches plus a fraction, rather than a measurement in millimeters,[9] or that foot-inch measurements are more suitable when distances are frequently divided into halves, thirds, and quarters, often in parallel.
[4] For most applications, the difference between the two definitions is insignificant – one international foot is exactly 0.999998 of a US survey foot, for a difference of about 1⁄8 in (3 mm) per mile – but it affects the definition of the State Plane Coordinate Systems (SPCSs), which can stretch over hundreds of miles.
The SPCSs were also updated, but the U.S. National Geodetic Survey left the decision of which (if any) definition of the foot to use to the individual states (and other jurisdictions).
[15] In 2019, the NIST, working with the National Geodetic Survey (NGS), National Ocean Service (NOS), National Oceanic and Atmospheric Administration (NOAA) and Department of Commerce (DOC), issued a Federal Register Notice (FRN) indicating the deprecation of the U.S. survey foot and U.S. survey mile units from December 31, 2022.
Note that as announced by the National Institute of Standards and Technology, the US survey foot, and other units defined in terms of it, have been deprecated since 2023, "except for historic and legacy applications".
However, use of definitions based on the U.S. survey foot should be avoided after December 31, 2022 except for historic and legacy applications.
The independence of the U.S. from the British Empire decades prior to the reformation of units in 1824—most notably the gallon, its subdivisions, and (in mass) higher combinations above the pound—is the cause of the differences in values.
The common 55-gallon size of drum for storing and transporting various products and wastes is sometimes confused with a barrel, though it is not a standard measure.
Water volume for sinks, bathtubs, ponds, swimming pools, etc., is usually stated in gallons or cubic feet.
The US dry gallon is less commonly used, and is not included in the handbook that many states recognize as the authority on measurement law.
[23][24] However pecks, or bushels are sometimes used—particularly for grapes, apples and similar fruits in agricultural regions.
There have historically been five different English systems of mass: tower, apothecaries', troy, avoirdupois, and metric.
Tower weight fell out of use in England (due to legal prohibition in 1527) centuries ago, and was never used in the U.S.
The pound avoirdupois, which forms the basis of the U.S. customary system of mass, is defined as exactly 453.59237 grams by agreement between the U.S., the United Kingdom, and other English-speaking countries in 1959.
To alleviate confusion, it is typical when publishing non-avoirdupois weights to mention the name of the system along with the unit.
The grain is used to describe the mass of propellant and projectiles in small arms ammunition.
In agricultural practice, a bushel is a fixed volume of 2,150.42 cubic inches (35.2391 liters).
Some nominal weight examples are:[26][27] The most common practical cooking measures for both liquid and dry ingredients in the U.S. are teaspoon, tablespoon, and cup, along with halves, thirds, quarters, and eighths of each.
