A slice of whole-grain bread weighs about 1 ounce. Each slice includes approximately 16 grams of whole-wheat flour and 12 grams of other ingredients. By definition, 1 ounce is 28.50 grams. With American coins, 11 pennies, six nickels, 12 dimes or five quarters all weigh approximately 1 ounce.
The U.S. weights and measures relate to the British imperial system that dates to the Romans and Anglo Saxons. However, before adopting the metric system, Great Britain redefined many of the units in 1824, while the United States retained the more traditional measurements. Among these measures was the ounce, which was 1/16 pound.
Until the early 1900s, the United States did little to set a standard for measures. Different regions developed different standards, which hindered trade between the states. In 1905, the National Bureau of Standards called for a meeting to discuss the differences. In 1915, the Bureau published its first model standards.
Jewelers weigh gold and other precious metals using the troy ounce. The troy ounce is 30.10 grams or slightly more than the standard ounce. The use of the term "ounce" in both weight and volume can cause confusion. The fluid ounce is 1/16 of a pint. When measuring water, both ounces are approximately the same. However, with other liquids, the density affects the weight of the fluid ounce.