Ask Felix: What's the Difference Between an Ounce and a Troy Ounce?

When weighing gold, you should always weigh in troy ounces (abbreviation is ozt). The troy ounce is derived from the Roman monetary system. To this day it is used to weigh precious metals. It is not the same as an avoirdupois ounce (the system we use to weigh just about everything else).

The troy ounce is heavier by about 9%. Thus, it takes 1.09 regular ounces to make a troy ounce. This is a very important distinction when buying or selling gold! The price of gold is always quoted in troy ounces. So if you were to buy gold weighed on a regular scale, you’d be getting less gold for your money.

Another oddity that comes to us from Rome is the symbol for pennyweight--dwt. The "d" stands for a denarius, which is a roman monetary unit that equates to about a penny. 

The chart below shows comparisons between various measurements used to weigh gold. You can use this as a conversion table.

1 ozt = 20 dwt

1 ozt = 31.1 grams

1 ozt = 480 grains

For example, say you have 10 grams of gold. You can use some simple math to convert that to other measurements.

10 grams / 31.1 = 0.32 ozt

0.32 ozt * 20 = 6.4 dwt

0.32 ozt * 480 = 153.5 grains