What is a Troy Ounce? Troy vs. Avoirdupois Weight, Weighing Precious Metals

Since many coins contain a precious metal, we expanded our website to include charts and spot prices of silver, gold and platinum (found here). In doing so, I was reminded of a common misconception many people have regarding the system of weight for precious metals. Many think an ounce of gold is the same “weight” as an ounce of beef. It’s not!

When you step on the scale, you don’t think of it but what’s being measured uses the system of weight known as avoirdupois. If we’ve lost a few pounds, we’d say something like, “I lost 2 pounds!” We wouldn’t say, “I lost 2 avoirdupois pounds!”

We’ve used the avoirdupois weight system in every day use for so long that we don’t even use its silly-seeming name. We can even break the system down. For example, most of us know there are 16 ounces in a (avoirdupois) pound.

What many don’t know or fail to remember is that silver, gold, platinum and other precious metals use the troy weight system. It’s completely different. When comparing the two systems – apples to apples – a troy ounce is heavier than an avoirdupois ounce – about 10 percent more. Or, more clearly, 10 troy ounces or 10 American Silver Eagles weigh more than a 10 ounce cut of steak.

Yet, and this is what can add to the confusion or what is often times forgotten, one troy pound weighs less than one avoirdupois pound. What… How!? Well, that’s ONLY because a troy pound has its own definition. One troy pound is defined as having 12 ounces – not the 16 ounces as defined in an avoirdupois pound.

This table may be useful:
 

Knowing how coins containing silver, gold or platinum stack up against our "every day" weight system isn’t super critical for a collector. But it doesn’t hurt either! Especially when so many collectible coins these days contain a precious metal.