ISO 9202 is the international standard published by the International Organization for Standardization that prescribes the fineness designations used to describe the precious-metal content of jewellery alloys. The standard establishes the recognised fineness levels for gold, silver, platinum, and palladium alloys and the conventions by which these are expressed in parts per thousand and as karat for gold. ISO 9202 is the technical foundation on which national hallmarking schemes set their permitted fineness levels and is the reference document for retail labelling of precious-metal jewellery in international trade.

Recognised fineness levels

For gold, ISO 9202 recognises the principal jewellery fineness levels of 999, 990, 916 (22 karat), 833, 750 (18 karat), 585 (14 karat), 375 (9 karat), and 333 (8 karat) parts per thousand. For silver, the recognised levels include 999, 958 (Britannia), 925 (sterling), 830, 800, and 720 parts per thousand. For platinum, the levels are 999, 950, 900, 850, and 800 parts per thousand. For palladium, the levels include 999, 950, 500, and selected lower values.

The standard's permitted fineness levels do not preclude the use of other levels in particular national markets, but they constitute the international reference set, and national hallmarking schemes typically draw their permitted levels from the ISO 9202 list, with occasional additions for historically established local levels.

Tolerance

ISO 9202 prescribes the tolerance with which the actual metal content must match the declared fineness. The standard requires that the actual content not fall below the declared fineness; positive deviation (where the metal contains more precious metal than declared) is permitted, while negative deviation is not. This creates the essential consumer-protection guarantee of hallmarking: a piece marked 18 karat (750) gold contains at least 750 parts per thousand of gold, and may contain slightly more, but not less.

Karat designation for gold

The karat designation for gold expresses fineness in twenty-fourths, with 24 karat representing pure gold (100 per cent or 999.9 parts per thousand in practice) and lower karats representing the corresponding fraction of gold in the alloy. The relationship between karat and parts per thousand is fixed: 22 karat is 916.6, 18 karat is 750, 14 karat is 583.3 (rounded to 585 in international standard), 9 karat is 375. ISO 9202 codifies the modern convention of expressing both the karat designation and the parts-per-thousand fineness on hallmarks where both are required.

Hallmarking and disclosure

National hallmarking schemes including the British Assay Offices, the French Bureau de Garantie, the Italian and Spanish authorities, and the Vienna Convention on the Control of the Fineness and the Hallmarking of Precious Metal Objects (CCM) all set their permitted fineness levels in alignment with ISO 9202. Retail tags and online listings of precious-metal jewellery typically use ISO 9202 designations, ensuring that consumers across markets can interpret a fineness mark consistently.

Related standards

ISO 9202 sits alongside the ISO 174 assay standards (ISO 11210, 11426, 11427, 15093, and others), the colour standard ISO 8654, the ring size standard ISO 8653, the disclosure standards ISO 18323 and 24016, and the quality management standard ISO 9001. The full set of standards constitutes the technical infrastructure of the international jewellery trade, and ISO 9202 specifically provides the fineness language that the rest of the system applies.