(Short) ton most commonly references its weight, the force exerted by its mass at standard gravity (i.e., short-tons-force). One short-ton contains 2,000 lbs-mass, which converted into slugs and multiplied by one standard gravity applies a 2,000 lb-force (see Newton's 2nd law of motion).
In the United States, a short ton is usually known simply as a "ton", without distinguishing it from the tonne (1,000 kilograms or 2,204.62262 pounds), known there as the "metric ton", or the long ton also known as the "Imperial ton" (2,240 pounds or 1,016.0469088 kilograms). There are, however, some U.S. applications where unspecified tons normally means long tons (for example, naval ships) or metric tons (world grain production figures).
Both the long and short ton are defined as 20 hundredweights, but a hundredweight is 100 pounds (45.359237 kg) in the U.S. system (short or net hundredweight) and 112 pounds (50.802345 kg) in the imperial system (long or gross hundredweight).
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In the United Kingdom, short tons are rarely used. The word "ton" is taken to refer to a long ton, and metric tons are distinguished by the "tonne" spelling. Most Commonwealth countries followed British practice with the exception of Canada, which used short tons as well as long tons. Canada now predominantly uses metric tons (tonnes).
20 hundredweights = 1 ton