What is millesimal fineness?

Millesimal fineness states a metal's purity in parts per thousand. A hallmark of 750 means 750 parts pure metal out of 1000, i.e. 75% pure, which for gold equals 18 karat. It is the modern international hallmarking standard.

How do karats relate to fineness for gold?

Karat measures gold purity in 24ths, so pure gold is 24 karat. To convert karat to fineness, divide by 24 and multiply by 1000: 18 karat = 18/24 × 1000 = 750. So 9 karat is 375, 14 karat is 585, and 22 karat is 916.

What does 925 mean on silver?

925 is sterling silver: 92.5% pure silver alloyed with about 7.5% copper for strength. It is the most common silver standard for jewellery and tableware. Higher grades include Britannia silver at 958 and fine silver at 999.

Why is platinum usually 950 and not 999?

Platinum jewellery is typically hallmarked 950 (95% pure) because a small amount of alloy such as ruthenium or cobalt improves workability and hardness while keeping the metal almost pure. Lower platinum standards of 900 and 850 also exist.

Does the converter store anything?

No. The table and karat/percentage converter run entirely in your browser. Nothing you enter is uploaded, logged or stored.

What is the Precious Metal Fineness & Hallmark Reference?

Reference table mapping precious-metal hallmark numbers (375, 585, 750, 925, 950, 999) to karat, percentage purity and common names for gold, silver, platinum and palladium, plus a fineness converter. It runs free in your browser on Gera Tools, with nothing uploaded.

Precious Metal Fineness & Hallmark Reference

Name: Precious Metal Fineness & Hallmark Reference
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Reading precious-metal hallmarks

A precious-metal hallmark states purity as a millesimal fineness — parts of pure metal per thousand. A gold ring stamped 750 is 75% gold (18 karat); silver stamped 925 is sterling. The same fineness numbers are used across gold, silver, platinum and palladium under modern hallmarking standards.

How it works

For gold, karat measures purity in 24ths, so fineness is karat ÷ 24 × 1000: 18 karat → 750, 14 karat → 585, 9 karat → 375. Silver, platinum and palladium are hallmarked directly in fineness, e.g. 925 sterling, 950 platinum, 999 fine. The percentage purity is simply the fineness divided by ten.

This reference lists the common hallmark numbers for each metal with their karat (where relevant), percentage and name, and includes a converter so you can turn any karat or percentage into a fineness figure and back.

Common hallmarks at a glance

Hallmark	Metal	Karat	Purity	Name
375	Gold	9 ct	37.5%	9 karat gold
585	Gold	14 ct	58.5%	14 karat gold
750	Gold	18 ct	75.0%	18 karat gold
916	Gold	22 ct	91.6%	22 karat gold
999	Gold	24 ct	99.9%	Fine gold
800	Silver	—	80.0%	Continental silver
925	Silver	—	92.5%	Sterling silver
958	Silver	—	95.8%	Britannia silver
999	Silver	—	99.9%	Fine silver
850	Platinum	—	85.0%	Platinum 850
900	Platinum	—	90.0%	Platinum 900
950	Platinum	—	95.0%	Platinum 950
500	Palladium	—	50.0%	Palladium 500
950	Palladium	—	95.0%	Palladium 950

What the alloy adds

Pure gold, silver, and platinum are soft and wear quickly in jewellery. The balance of the fineness (the non-pure portion) is the alloy added for hardness and workability:

Gold — typically alloyed with silver, copper, zinc, or palladium. The alloy ratio and choice determines colour: more copper → rose gold; added silver and reduced copper → white gold (though true white gold usually also has rhodium plating); palladium → platinum-white.
Sterling silver (925) — traditionally 7.5% copper, which hardens the metal and gives it durability. Silver-copper alloys tarnish faster than fine silver.
Platinum 950 — typically alloyed with ruthenium, cobalt, or iridium for hardness.

Tips and example

A bracelet stamped 585 is 14 karat gold, 58.5% pure. A spoon stamped 958 is Britannia silver. To go the other way, 22-karat gold converts to 22 ÷ 24 × 1000 = 916.7, hallmarked 916. Remember the hallmark certifies the pure-metal content, not the weight or value of the whole item. Hallmarking requirements differ by country — in the UK the Assay Office stamps are required by law for items above minimum weight thresholds; in some other markets self-declaration is accepted.