Millesimal fineness is a system of denoting the purity of platinum, gold and silver alloys by parts per thousand of pure metal in the alloy.

For example, an alloy containing 75% gold is denoted as "750".

It is an extension of the older carat (karat in North American spelling) system of denoting the purity of gold by fractions of 24, such as "18 carat" for an alloy with 75% (18 parts per 24) pure gold.

The millesimal fineness is usually rounded to a three figure number, particularly where used as a hallmark, and the fineness may vary slightly from the traditional versions of purity.

The most common millesimal finenesses used for precious metals are:

Platinum

• 999 (also known as three nines fine)
• 950 (the most common purity for platinum jewellery)
• 900 (also known as one nine fine)
• 850

Gold

• 999 (Fine gold equivalent to 24 carat, also known as three nines fine)
• 990 (also known as two nines fine)
• 916 (equivalent to 22 carat)
• 833 (equivalent to 20 carat)
• 750 (equivalent to 18 carat)
• 625 (equivalent to 16 carat)
• 585 (equivalent to 14 carat)
• 417 (equivalent to 10 carat)
• 375 (equivalent to 9 carat)

Silver

• 999 (Fine silver used in bullion bars, also known as three nines fine)
• 958 (equivalent to Britannia silver)
• 950 (equivalent to "Mexican silver")
• 925 (equivalent to Sterling silver)
• 900 (equivalent to "Coin silver" in the USA, also known as one nine fine)
• 833
• 800

See also

• Gold as an investment
• Gold coin
• Silver as an investment
• Silver coin
• Platinum coin

Gold | Silver | Gold investments | Numismatics | Jewellery | Jewellery making | Units of purity