It’s very important to know some basic weight terms if you want to understand charts and discussions and news reports about precious metals and gemstones.  Therefore, I’ve provided for you a concise glossary of terms below: avoirdupois ounce, troy ounce, grain, and pennyweight.

NOTE:  While most of the world uses the metric system, the United States primarily uses the U.S. customary system (also called the American system) to measure weight.

Avoirdupois ounce is abbreviated oz.

1 avoirdupois ounce = .911458333 troy ounces, 437.5 grains or 28.349523125 grams

Definition of Troy Ounce

Gemstones and precious metals such as gold, silver, and platinum are sold by the troy ounce.  It is heavier than the avoirdupois ounce.

Troy ounce is usually abbreviated t oz or sometimes oz t.

1 troy ounce = 1.097142857 avoirdupois ounces, 20 pennyweights, 480 grains, or 31.1034768 grams

1 kilogram  = 32.15 troy ounces

NOTE:  There are 12 troy ounces in a troy pound, as opposed to 16 avoirdupois ounces in an avoirdupois pound.  Therefore, a troy pound is lighter than an avoirdupois pound.  However, the troy pound is no longer being used which helps a lot!

Definition of Grain

A grain is a unit of weight in both the U.S. customary system and the troy system that weighs the same under both systems. Its abbreviation is gr.

1 unit of grain = 0.002285 ounces or 0.06479891 grams

Definition of Pennyweight

Jewelers use the pennyweight in calculating the amount and cost of precious metals used in fabricating or casting jewelry.  Dentists still use the pennyweight as the measure of precious metals in dental crowns and inlays.  It has no relation to penny coins.

Pennyweight is usually abbreviated dwt or pwt, and occasionally PW. Why is dwt the most common abbreviation? The “d” was taken from the ancient Roman penny-like coin denarius and was the abbreviation for the penny before the decimalization of the British monetary system.  Then it was used as an abbreviation for pennyweight and still is.

20 pennyweights = 1 troy ounce

1 pennyweight = 1/20 of a troy ounce, 24 grains, 7.777 carats, approximately 0.055 ounces, or 1.55517384 grams

How to Convert Avoirdupois Ounces to Troy Ounces

Multiply the number of ounces x .912 to get the approximate number of troy ounces; for example, 4.50 ounces x .912 = 4.10 troy ounces.

In Conclusion

Well, I hope you found this introduction helpful!  Let me know if you enjoyed this information or if there is something I can add to it to make it easier to understand or better in any way.  Thanks!

Tags: American system, avoirdupois ounce, definition of grain, definition of pennyweight, definition of troy ounce, Gemstones, metric system, precious metals, sell gold, troy ounce, U.S. customary system