How to Convert Troy Weight Measurements
Troy weight derives its name from the French city Troyes. This system of measurement is used for weighing gunpowder, arrows, arrowheads, gemstones and precious metals, such as gold or silver. Here are definitions for each troy weight unit. The steps demonstrate how to convert between troy and avoirdupois weight and how to convert to metric mass units.
- Difficulty:
- Moderate
Instructions
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Basic Troy Weights
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1
Divide the number of grains by 24 to get the number of pennyweights (abbreviated dwt).
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2
Convert pennyweights to ounces troy by dividing by 20. There are 480 grains in an ounce troy.
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3
Change ounces troy to pounds troy by dividing by 12. There are 240 pennyweights in a pound troy, and 5,760 grains in a pound troy.
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4
Abbreviate pound troy as "lb t" and ounce troy as "oz t" to distinguish them from the more common avoirdupois pound and ounce.
Converting Avoirdupois Weight to Troy Weight
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1
Multiply ounces avoirdupois by 0.911 to get the equivalent number of ounces troy. To convert ounces troy to ounces avoirdupois, multiply by the reciprocal of 0.911, which is 1.098.
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2
Convert pounds avoirdupois to pounds troy by multiplying by 1.1215. To convert pounds troy to pounds avoirdupois, multiply by the reciprocal of 1.1215, which is 0.823. One pound avoirdupois equals 14.58 ounces troy.
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3
Change pennyweights to drams avoirdupois by multiplying by 1.14 and drams avoirdupois to pennyweights by 0.878. There are 16 drams avoirdupois in one ounce avoirdupois.
Converting Troy Weight to Metric Equivalents
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1
Equate one grain to 64.799 milligrams. A grain is the same size, whether in troy weight, avoirdupois weight, or apothecary weight.
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2
Convert pennyweights to grams by multiplying by 1.555 or to milligrams by multiplying by 1555.
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3
Change ounces troy to grams by multiplying by 31.103.
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4
Get the metric equivalent of pounds troy in grams by multiplying by 373.242, or in kilograms by multiplying by 0.373242.
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1
Tips & Warnings
The above system was developed by the British. The Scots used a system with multiples of 16: 16 drops to the troy ounce, 16 ounces to the troy pound and 16 pounds to the troy stone.
The system of 240 pennyweights to the pound troy and 20 pennyweights to the ounce troy paralleled the original British monetary system of 240 pence to the pound and 20 pence to the shilling.
Milligrams, grams and kilograms are actually metric units of mass, which is simply how much stuff composes an object. Weight is defined as the force of gravity acting on an object. At the earth's surface, however, this distinction is moot.
