International yard and pound

The 1959 agreement among six countries defined the international yard as exactly 0.9144 metres and the avoirdupois pound as exactly 0.45359237 kilograms.

1959 International Yard and Pound Agreement: An agreement adopted in 1959 that fixed exact metric equivalents for the yard and avoirdupois pound. This is the agreement that established the international definitions.
Yard: A unit of length equal to three feet or 36 inches. The agreement fixes the yard’s length through an exact metric value.
Unit conversion: The process of expressing a quantity in a different measurement unit without changing its value. The agreement supplies exact factors for converting yards and pounds to metric units.
Pre-1959 United States yard: The United States yard standard used before adoption of the international yard in 1959. Its slight difference from the new definition mattered in high-precision surveying.
United States customary units: A system of measurement units used in the United States, including the customary yard and pound. The United States adopted the agreement alongside other English-speaking countries.
Pound (mass): A unit of mass used in customary and imperial measurement systems. The agreement standardizes this unit as a precise fraction of a kilogram.
International System of Units: The internationally standardized system of measurement built around seven base units. Metric units in the agreement connect customary measures to the global measurement system.
U.S. survey foot: A former U.S. length unit defined as exactly 1200/3937 metres. It remained distinct from the international foot after the agreement, until its retirement for most uses.
Imperial units: A system of units established in Britain in 1824, including the yard and pound. The agreement aligned key British measures with the shared international standards.
Avoirdupois system: A system of weights based on the avoirdupois pound of 16 ounces. The pound in the agreement is specifically the avoirdupois pound.

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