Unit Conversions and Descriptions

Precious metals are bought and sold in troy ounces and grams.

When someone speaks of something weighing an ounce, the chances are, that they are referring to an Avoirdupois Ounce. Unless, they are referring to an ounce of gold, silver, platinum, gemstones or gunpowder. In which case, they are referring to a Troy Ounce. The two ounces are not the same!

The avoirdupois system is a system of weights or mass based on a pound of sixteen ounces. It is the everyday system of weight used in the United States. It is still widely used by many people in Canada and the United Kingdom despite the official adoption of the metric system.

The pennyweight is an archaic weight used in the valuation and measurement of precious metals. Jewellers may still use the pennyweight in calculating the amount and cost of precious metals used in fabricating or casting jewelry. Similarly, dentists and dental labs may also use the pennyweight as the measure of precious metals in dental crowns and inlays.

A pennyweight is a unit of mass which is 24 grains, 1/240th of a troy pound, 1/20th of a troy ounce, approximately 0.055 ounces or approximately 1.555174 grams.

Carat is a unit of mass for gemstones and pearls, equal to 0.2 gram or 200 milligrams. Art is a unit of purity for gold, where one art is 1/24th purity by mass.

Grains are currently used in the United States and Canada to measure the mass of bullets and gunpowder, and scales for handloading measure in grains; bullets are generally measured in increments of 1 grain, gunpowder in increments of 0.1 grains. An avoirdupois ounce is equal to 437.5 grains, whereas a troy ounce is equal to 480 grains.

The Tola, is a traditional Ancient Indian and South Asian unit of mass, now standardised as 180 troy grains (11.6638038 grams) or exactly 3/8 troy ounce.

The most common solid gold hallmarks are the art stamps; 8k, 9k, 10k, 14k, 18k, 21k, 22k. Other hallmark stamps include; 333, 375, 417, 583, 585, 750, 875, 916, 917, 999. These all represent the permillage gold or "fineness" in the alloy of the item, 333 being 33.3% or 8/24ths gold (8k), 417 being 41.7% or 10/24ths gold (10k) etc.

One troy ounce [ozt] is exactly:

  • 31.1034768 grams [g]
  • 20 pennyweights [dwt]
  • 480 grains [gr]
  • 2.66666666... tolas [tola]
  • 0.0685714285714 pounds [lb]
  • 0.0311034768 kilograms [kg]
  • 0.08333333... troy pounds [lb t]

One avoirdupois ounce [oz] is exactly 28.349523125 grams or 437.5 grains [gr]

One pennyweight [dwt] is approximately 1.555174 grams

One grain [gr] is exactly 0.06479891 grams

One carat [ct] is exactly 0.2 grams. The carat is divisible into one hundred points of two milligrams each.

One troy pound [lb t] is exactly 12 troy ounces [ozt], 5,760 grains [gr], 0.822857142857 pounds [lb] or 373.2417216 grams [g]

One pennyweight [dwt] is exactly 24 grains [gr], or 1.55517384 grams [g]

One avoirdupois pound [lb] is exactly 16 avoirdupois ounces [oz], 7000 grains [gr] or approximately 14.5833333333 troy ounces [ozt]

One tola [tola] is exactly 180 troy grains [gr], 11.6638038 grams [g], 7.5 pennyweight [dwt], 3/8 troy ounces [ozt]