Pennyweight to Grams Converter

The conversion, and why the exact figure matters

The troy ounce has been defined as exactly 31.1034768 grams since the international yard and pound agreement of 1959. Twenty pennyweights make a troy ounce, so:

• 1 pennyweight = 1.55517384 g — exact, not rounded
• 1 gram = 0.643014931 dwt
• 1 troy ounce = 20 dwt = 480 grains = 31.1034768 g
• 1 pennyweight = 24 grains

Plenty of tables round the pennyweight to 1.555 g. That loses about 0.17 milligrams every pennyweight — three and a half milligrams across a 20 dwt piece. It is a tiny amount, and it always falls in the buyer’s favor, but the real point is simpler: this is the one number that is exactly defined, so there is no reason to round it at all.

Why jewelers weigh in pennyweights at all

Habit, and a useful one. The pennyweight is a convenient size for the things a jeweler handles: a plain wedding band is a few pennyweights, a heavy chain a few dozen. It also keeps the arithmetic honest — twenty of them to the troy ounce, and the troy ounce is the unit gold is priced in worldwide. A buyer who quotes you “per pennyweight” is quoting one twentieth of the spot price, less their margin.

The trap: troy ounces are not the ounces on your kitchen scale

A troy ounce is 31.1034768 g. The everyday avoirdupois ounce is 28.349523125 g — about 10 % lighter. Precious metals are sold in troy; almost everything else is sold in avoirdupois. Weighing gold on a scale set to ordinary ounces and pricing it per troy ounce overstates the value by roughly a tenth. The converter above includes both so you can see the gap.

Now put a price on it

This page converts weight; it does not price anything, because a unit conversion is a fixed fact and a price is not. Once you know the weight, the gold calculator and the silver calculator take pennyweights directly and apply today’s spot price with its timestamp.