Some of the early measurements of weight included the grain, pound, and ton. Ancient peoples used stones, seeds, and beans to measure weight, but grain (such as wheat or barleycorn) was a favorite. In fact, the grain (abbreviated “gr”) is still one of the smallest units of weight used today (to compare, one pound equals 7,000 grains).

The traditional pound as a unit of weight was used throughout the Roman Empire. But like many other measurements over time, the number of ounces in a pound seemed to shift and change. For example, the number of ounces in the Roman pound was 12; European merchants used 16 ounces to the pound. Eventually, 16 ounces in a pound became standard (for more about ounces, see below).

Back in the 19th century, the Americans—who did not like the British larger weights—decided that a hundredweight would equal 100 pounds (the British hundredweight was 112). This meant a ton was equal to 20 hundredweight for the American ton (or the American’s short ton was 2,000 pounds), while the British long ton of 20 hundredweight was equal to 2,240 pounds. There were, of course, debates, but not everyone disagreed with the American short ton. It became the favorite of British merchants, who called it a cental. Eventually, the ton on the international market “went metric,” and today a metric ton is close to the original British long ton. It is equal to 1,000 kilograms, or approximately 2,204 pounds, and is officially called tonne. Although the International System (SI; see below) standard uses tonne, the United States government recommends using the metric ton.