United States customary units

United States customary units
Name	United States customary units
Type	customary system
Regions	United States
Subunits	inch, foot, yard, mile, ounce, pound, ton, gallon, quart, pint, cup, fluid ounce, teaspoon, tablespoon

United States customary units are a system of measurements historically derived from English units used in the United Kingdom and adapted in the Thirteen Colonies prior to the formation of the United States. The system remains used in everyday life, commerce, and several industries across the United States of America despite the international prevalence of the International System of Units and the influence of metrication efforts associated with organizations such as the International Bureau of Weights and Measures, the National Institute of Standards and Technology, and legislative initiatives like the Metric Conversion Act of 1975. Debates over persistence of the system have involved actors including the United States Congress, state governments such as California and Texas, and professional bodies like the American Medical Association.

History

Customary units trace to medieval English practice influenced by statutes like the Assize of Weights and Measures and the Exchequer's standards, later evolving through legal instruments such as the Weights and Measures Act 1824 in the United Kingdom and colonial ordinances in Virginia and Massachusetts Bay Colony. Following independence, the United States Congress enacted measures to standardize units, including debates in the Continental Congress and proposals by figures associated with the Founding Fathers and early national institutions such as the United States Mint and the Survey of the Coast. Nineteenth-century developments, including the adoption of the yard and pound definitions tied to physical prototypes stored in repositories akin to the British Standards Institution, shaped the system. Twentieth-century international agreements like the Treaty of the Meter and the establishment of the International System of Units prompted metrication movements, while federal legislation like the Metric Conversion Act of 1975 and later executive actions influenced but did not fully replace customary practice.

Units and definitions

The system comprises length units such as the inch, foot, yard, and mile; mass units like the ounce (avoirdupois), pound (mass), and short ton; and volume units including the gallon (United States), quart (United States), pint (United States), and fluid ounce (United States). Area and derived units such as the square foot and acre are widely used in land measurement, with survey-specific units like the United States survey foot formerly employed by agencies including the United States Geological Survey and the Bureau of Land Management. Definitions over time referenced standards such as the international yard and pound agreement and national prototypes maintained by the National Institute of Standards and Technology and earlier by the United States Coast and Geodetic Survey.

Usage in the United States

Customary units are prevalent in sectors ranging from construction overseen by organizations like the Associated General Contractors of America to retail regulated by the Federal Trade Commission and food service standards used by entities such as the United States Department of Agriculture and the Food and Drug Administration. Everyday consumer contexts—road signage managed by the Federal Highway Administration, real estate listings in states like Florida and New York, and aviation practices involving carriers such as American Airlines—rely on customary measures for distance, area, and volume. Education debates involve institutions such as the Department of Education and professional societies like the American Society of Civil Engineers and American Meteorological Society, while sports organizations including the National Football League and Major League Baseball use yard-, foot-, and inch-based measurements for fields and equipment.

Comparison with the International System of Units

The International System of Units (SI) offers coherent base units like the metre, kilogram, and second adopted by international bodies such as the International Organization for Standardization and the International Electrotechnical Commission. SI coherence contrasts with customary unit relationships that require conversion factors (for example, 12 inch = 1 foot, 3 foot = 1 yard', 5280 foot = 1 mile). Scientific research institutions including the National Institutes of Health, the Centers for Disease Control and Prevention, and universities such as Massachusetts Institute of Technology typically publish in SI, creating dual-unit reporting requirements for journals like those of the American Chemical Society and bodies such as the National Academy of Sciences. International trade partners, including the European Union, Japan, and Canada, use SI for regulation and standards, necessitating interoperability for exporters and importers like multinational corporations General Motors and Procter & Gamble.

Legal status and standards

Federal law and agency regulations address measurement standards: the United States Congress delegates custody of national measurement standards to the National Institute of Standards and Technology under acts influenced by international treaties like the Convention of the Metre. Consumer protection laws enforced by the Federal Trade Commission and state statutes administered by offices such as the California Department of Food and Agriculture specify labeling and sale units. The Uniform Packaging and Labeling Regulation and industry standards from bodies like the American National Standards Institute interact with customary usage; courts, including the Supreme Court of the United States, have adjudicated disputes involving measurement standards in commerce and taxation.

Conversion and interoperability issues

Conversion challenges affect sectors from manufacturing companies like Boeing and Caterpillar to healthcare providers represented by the American Medical Association and shipping firms such as United Parcel Service and FedEx. Historical incidents—most famously the loss of the Mars Climate Orbiter—illustrate risks when systems intermix; regulatory frameworks by the Federal Aviation Administration and Occupational Safety and Health Administration address related safety and compliance. Software and information standards bodies like the Institute of Electrical and Electronics Engineers and the Internet Engineering Task Force provide guidance for unit encoding, while trade agreements with partners including Mexico and Canada necessitate harmonized labeling and measurement conversion to facilitate logistics, standards conformity, and consumer protection.

Category:Measurement systems