How can a Troy Ounce be more than an ounce ?
Precious metals such as gold
and silver are often sold by the troy ounce. Many people don’t realize
that an ounce of gold is more than the typical ounce found at the grocery
store. In many English speaking countries there are two systems for
measuring weight.
One, for precious metals,
called the troy ounce.
The other is for
Commodities such as sugar, grains, and the typical grocery items. It is called
the avoirdupois ounce. Here in the USA we often use the avoirdupois
ounce. Every time you step on the scale at home, or weight food found in the
grocery, you use the avoirdupois ounce weight system. There are 16 avoirdupois
ounces in a pound.
Avoirdupois weights -
An Avoirdupois pound is equal to about 453.6 grams, or 14.583 troy ounces. 1
avoirdupois ounce = 437.5 grains, or 28.35 grams. 1 avoirdupois pound
equals 16 (avoirdupois) ounces or 453.59 grams. That is the equivalent to
14.58 "troy" ounces.
So what do you get when you
buy an ounce ?
The troy ounce is heavier
than the typical grocery store (avoirdupois) ounce used in the USA. When you
purchase a 1 ounce silver or gold coin, you are receiving a "troy"
ounce. If you put that same 1 troy oz. coin on a grocery store scale you will
find that it weighs about 10% more than the food ounce you are familiar with.
It will weigh about 1.1 avoirdupois ounces. Consequently, a grocery store
pound which weighs 16 avoirdupois ounces (or 453.59 grams) will contain about
14.58 troy ounces.
Separately, the troy weight
system has it's own definition of a "troy" pound. A "troy
pound" contains 12 troy ounces or 373.24 grams (which is over 13
avoirdupois ounces).
It is thought that the troy
ounce was named after a weight system used in Troyes France during the Middle
Ages.
Troy weights - One troy
ounce = 480 grains, or 31.10 grams.
There are also 20
pennyweights to a troy ounce. A troy pound contains 12 troy ounces (over 13
avoirdupois ounces) and is equivalent to 373.24 grams. 32.15 troy ounces
= 1 kilogram.
Perhaps an easy way to compare Troy ounces versus
avoirdupois ounces is to look at how they weigh using the metric system.
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One troy ounce weighs 31.1 grams |
One avoirdupois ounce weighs 28.35 grams |
How to convert regular (avoirdupois) ounces to a troy ounce
Use this formula for an approximation to convert grocery store type weights to troy ounces. Multiply # regular ounces X .912 to get approximate # troy ounces Examples: A grapefruit weighs 4.5 avoirdupois ounces. 4.50 x .912 = 4.10 troy ounces. Ten troy ounces are equivalent to about 10.96 regular ounces. Because each troy ounce is heavier, it would take almost 11 regular ounces to equal ten troy ounces. |
Conversion Table
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