In the United States, a "quarter" is a common informal term used to refer to a quarter of various units of measurement, such as a quarter of a dollar, a quarter of a year, or a quarter of other divisible quantities. However, when used in the context of weight or mass, a "quarter" typically refers to a quarter of a hundredweight (cwt).
Since a hundredweight (cwt) in the United States is equal to 100 pounds (lbs), a quarter of a hundredweight is equal to:
1 quarter (US) = 25 pounds (lbs)
So, when you see "quarter" used in the context of weight or mass in the United States, it generally means 25 pounds. This term is often used informally, especially in agricultural or trade contexts, to refer to a convenient fraction of weight.
The kilogram (kg) is the base unit of mass in the International System of Units (SI). It is defined as the mass of the International Prototype of the Kilogram (IPK), a platinum-iridium cylinder kept at the International Bureau of Weights and Measures (BIPM) in France.
Until May 20, 2019, the kilogram was defined by the physical prototype, but as part of the redefinition of the SI units, the kilogram was redefined in terms of fundamental constants. Since that date, the kilogram is defined by fixing the numerical value of the Planck constant (h) to be exactly 6.62607015 x 10^-34 joule-seconds.
This redefinition ensures that the value of the kilogram is now based on a constant of nature rather than relying on a physical object that could potentially change over time. It allows for a more precise and stable definition of the kilogram and other SI units.