What’s the Diff?
What’s the difference between 1 troy ounce of gold and 1 (regular) ounce? What’s the difference between 18 and 10 karat gold? Let me explain.
What’s a “Karat”
The term “karat” is used to describe the unit of measurement for the proportion of gold (i.e. % purity of the gold content) in a piece of jewelry, coin, ingot or bar.
Gold will often be mixed with “filler metals” such as silver, palladium, platinum, nickel and even copper to combat the softness of pure 24 karat.
- Gold that contains a degree of silver, platinum or palladium is referred to as “white gold”.
- Gold that contains copper is gives gold durability and a golden rosy tone.
Below is a table outlining the karat designations at various gold purity levels plus the extent of “fineness” as is used in some countries such as Italy.
| Karat/Fineness | Gold Content [Purity] |
| 24 karat | 99+% |
| 22 karat/917 | 91.6% |
| 21 karat | 87.5% |
| 20 karat | 83.3% |
| 18 karat/750 | 75.0% |
| 15 karat | 62.5% |
| 14 karat/583 | 58.5% |
| 10 karat/417 | 41.7% |
| 9 karat | 37.5% |
| 8 karat | 33.3% |
| 1 karat | 4.2% |
In some countries “karat” and “carat” are used almost interchangeably although, strictly speaking, the words’ correct meanings are defined as:
- karat: the % purity of precious metal content
- carat: the weight of a gemstone
100% pure gold is defined as having a purity of 24 karats so if something is 24 karat gold then it’s made of gold and nothing else – regardless of size…
Gold is a relatively soft metal and high-karat gold tends to be easily damaged and, as such, a 24 karat item is usually reserved for display or ceremonial use as the picture of me with “my” 100kg. Canadian Maple Leaf 99.99999% pure gold coin which is now worth in excess of $7,700,000 USD! (100kg. x 32.1507466 troy oz. x $2,400/ozt. USD)
- All jewelry is required by law to be stamped so consumers will know the quality of gold used. Jewelry made in North America is typically marked with the karat grade (10K, 14K, etc.), and jewelry made in Italy is typically marked with the “fineness” such as (417, 583, etc.). Most retail gold items have a karat rating in the range 9 to 18. In the U.S. the minimum karat value for an item to be sold as gold jewelry is 10. In the U.K. 9 karat is more common.
The number 24 may have originally been chosen to represent pure gold because it divides evenly by 2, 3, 4, 6, 8 and 12. Thus it’s easy to talk about a gold item being half pure (12 kt), 2/3 pure (16kt) etc. 9 karat would thus be 3/8 gold, 18 karat would be 6/8 (i.e. 3/4).
What’s a “Troy” Ounce
A troy ounce (ozt) is a unit of imperial measure most commonly used to gauge the weight and therefore the price of precious metals.
One troy ounce is equivalent to 1.09714 avoirdupois (our conventional every day measurement) ounces i.e. 9.714% greater in weight and 1 kg. consists of 32.1507466 troy oz.
Please keep the distinction between ounces and troy ounces in mind when buying small quantities of gold and/or silver.
What Does “ozt” Mean?
The abbreviation “ozt” is a shortened way to write “troy ounce”, and refers to the % purity of the content of the precious metal.
Conclusion
Never again will you be misled when reading about or considering the purchase of any item in which the terms karat, or troy ounce are – often loosely – used.