The Troy Ounce—The Standard for
Precious Metals

You buy food in grams or ounces/pounds (in the US). But you buy precious metals by the troy ounce, part of the troy weights system. But why the difference? What is a troy ounce, and how is it used?

Historians believe that the troy ounce is named after the city of Troyes, France, which had its own weight system during the Middle Ages. That system became know as troy weights.

A troy ounce weighs more than a regular ounce, also known as the avoirdupois ounce. The ratio is just slightly less than 1.1 to 1. The easiest way to compare the two is by converting their weights to grams (the metric system).

Ounce to Ounce, Who's the Heavyweight?

The troy ounce weighs 31.10 grams. The avoirdupois ounce weighs in at 28.35 grams. So a silver coin weighing one troy ounce weighs 31.10 / 28.35, or 1.097, ounces. Rounding up, which most people do for quick coin calculations, the typical silver bullion coin weighs 1.1 avoirdupois ounces.

The main thing to remember is that when you're buying silver coins or gold coins, you're buying more than a regular ounce. And the price you're quoted is for more than a regular ounce. The weight and the spot price are based on the troy ounce.

Are you ready to be confused some more?

Pound to Pound, Who's the Lightweight?

Note

At least one 4 ounce silver coin is marked as weighing a quarter pound. This is inaccurate.

A 4 ounce coin weighs 4.4 avoirdupois ounces, which puts it at slightly more than a quarter pound (4.4 / 16).

However, since the proper measurement is troy pounds, this coin is, in reality, one third of a troy pound (4 / 12).

While the troy ounce is heavier than the regular ounce, the troy pound is lighter.

There are only 12 ounces in a troy pound, while there are 16 ounces in a regular pound. Comparing by grams makes it easier to compare them.

The troy pound weighs 373.24 grams (12 * 31.10). The avoirdupois pound weighs 453.59 grams (16 * 28.35). So the troy pound weighs just 82.29% of the regular pound.

When Do I Need the Troy Ounce Weight?

There are two times that you'll need to remember troy ounce calculations—when buying junk silver and when traveling with your precious metals.

Airlines have weight restrictions. If you fly with a large number of silver or gold coins, you could be overweight if you miscalculate the weight of your coins. Remember to add 10%.

Of course, you should never carry your coins in your checked baggage. Carry them in your pockets or in your carry-on piece or your computer bag or purse.