The old riddle goes: what weighs more a pound of feathers or a pound of gold? Some say gold because it is heavier. Others say they are both a pound so they weigh the same. Both are wrong. How can this be? Tradition. Gold is not weighed in the ordinary weights. Gold is weighed in the troy measurement system. One ounce of gold is not the same as the ordinary ounce (really called avoirdupois ounce).
The best way to understand this is to convert them both to a uniform system. A gram or gramme is a standard metric unit of mass. An avoirdupois ounce converts to 28.34 grams approximately. The troy ounce is 31.1 approximately. You say, “Aha! Gold weigh more, so a pound of gold weighs more than a pound of feathers.” Unfortunately there is one more piece of the puzzle. We all know 16 ounces equal a pound. True in the avoirdupois system, but not in the troy. In the Troy system only 12 ounces equal a pound. So a pound of feathers weighs 453.59 grams approximately and a pound of gold weighs 373.24 approximately. So a pound of feathers weighs more then a pound of gold.
Some say gold because it is heavier. Others say they are both a pound so they weigh the same. Both are wrong.
There is more trivia about gold weights. The troy system historically was used for measuring the weight of drugs, precious metals and gemstones. The name comes from the French city of Troyes. The noble metals (gold, silver and platinum) all use the troy system. A troy ounce is 20 pennyweights. The pennyweight was the weight of a silver penny in medieval England. When pennies were introduced in England in the 8th century, their original weight is believed to have been 24 grains. This was gradually reduced, in at least thirteen stages until it reached 7.27 grains by 1816. 24 grains = 1 pennyweight and 20 pennyweights = 1 ounce troy.
Even more trivia if you’d like to read on. “Grain is an ancient unit which was originally based on the weight of a grain of wheat. The grain is the smallest unit of weight in the avoirdupois, troy, and apothecaries systems. Surprisingly it is identical in all three systems.” 4 grains = 1 carat; 24 grains =1 pennyweight; 480 grains = 1 troy ounce; 15.432 grains = 1 gram.
“Although we have stated above that the grain weighed the same in all three of the above systems, there were at least two different grains. The troy system used the supposed weight of the barley grain, whereas the wheat grain was also used as a standard of weight. There were three barley grains to four wheat grains.”
That is enough trivia for now. If you wanted to update the old riddle, you could say: what weighs more, a kilo of feathers or a kilo of gold?