Abacus
Antique Dealers: Guide to Precious Metals and
Gemstones Weights and Measures
This
page explains weights and measures used for gold,
silver, and precious stones. Discusses grams, pennyweight,
troy ounces, carats and karats. Includes handy conversion
charts and valuing tips. If you like collecting jewelry
or silver, you should have a copy of this reference.
Uploaded by the author, a jewelry dealer and gemologist.
Troy
Weight - gold and silver are measured in Troy weight,
a system that includes pennyweights, ounces and pounds.
The ounces and pounds do not equal the Avordupois
or customary U.S. system that other common goods are
measured in. For example a troy ounce weights about
10 percent more than a Avordupois ounce.
24
grains = 1 pennyweight = 1.5552 grams
20 pennyweight = 1 troy ounce = 31.1035 grams
12 ounces = 1 pound troy = 373.24 grams.
Gold is also commonly measured in metric grams.
Precious
stones are measured in carats with a carat being 200
milligrams or 1/5 of a gram. Carats are further broken
down into “points” which are 1/00 of a carat.
Note that Karat with a “K” is a measure
of the purity of a gold alloy and is discussed separately
below.
The
conversion table below will show you how to convert
from avordupois to troy to metric, and to and from
units within each of the systems.
The
table can be especially handy if you don’t have
the proper scale to use. However you must be sure
your scale is sensitive enough for the job. It’s
fine to use an accurate postal scale to weigh a piece
of silver that weighs several ounces and then make
the conversion to troy weight, but don’t try
to weigh a piece of gold that weighs only a few grams
using a postal scale. Similarly, if you are trying
to weigh a diamond to the nearest 1/100 of a carat,
which is how diamonds are measured, use a scale with
carat precision or a gram scale that is accurate to
at least .002 gram. Note that when converting from
one system to another, there will be slight rounding
errors of a fraction of a percent.
Weight
Conversion Chart for Silver, Gold and Gems
To convert:
Avordupois Ounces to Troy ounces multiply by .91
Avordupois Ounces to pennyweight multiply by 18.2
Avordupois ounces to grams multiply by 28.35
Troy ounces to grams multiply by 31.1
Troy ounces to pennyweight multiply by 20
Troy ounces to pounds troy, divide by 12
Pennyweight to grams multiply by 1.56
Pennyweight to troy ounces multiply by .05 (or divide
by 20)
Grams to pennyweight multiply by .64
Grams to troy ounces multiply by .032
Grams to carats multiply by 5
Carats to grams multiply by .2 (or divide by 5)
Carats to “Points” multiply by 100.
“Points” to carats multiply by .01 (or divide
by 100)
Karat designation for gold refer to the number of
parts per 24 that is pure gold. Thus 14K is 14/24
pure gold, while 10K is 10/24 pure gold. Please note,
however, that if a piece of jewelry is marked something
like “1/20 14K G.F” this means that it is
gold-filled, and 1/20 of the weight of the piece is
the layer of 14K gold on the outside of the piece.
In this case you must divide the weight of the piece
by 20, and then apply the formula in the chart below.
The following chart shows how to find the weight of
pure gold present in each common alloy of gold used
in jewelry.
To
find the weight of gold in:
9K multiply weight by .375
10K multiply weight by .417
12K multiply weight by .50
14K multiply weight by .583
15K multiply weight by .625
18K multiply weight by .75
Note that if you have a piece of European gold which
is marked directly with the percentage, for example
585, or 750 just put the decimal point in front of
the numbers and multiply by the weight to get the
gold content.
If you look up the current gold spot price in the
newspaper, you can get an idea of the intrinsic value
of an article as an aid in establishing its value.
Note,
however, that if you are scrapping an item, you will
never get spot for it, but only a percentage of spot
to allow for processing. Many collectible pieces,
of course, are worth more than their scrap value.
Jewelry sold new in stores is always sold at a price
above gold value to cover labor and profits at the
various stages in the distribution channel.
