mass fraction / fineness · Jewelry / precious metals · Historical-modern
Karat value k corresponds nominally to k/24 gold by mass; 18K = 75% = 750 parts per thousand.
Converter
mass fraction / fineness · Precious metals / assay · Modern
millésimal fineness
exact
- Record
- M557
- Definition quality
- Standardized
- Conversion mode
- formula
- Calculator
- Formula-based
Definition
Fineness in parts per thousand = pure precious metal mass / total alloy mass × 1000. 750 = 75% = 18K nominally.
Reference value
millésimal fineness converts through a formula rather than a simple multiplier.
History & use
Hallmarks commonly use fineness-style numbers because they state the alloy fraction more directly than a 24-part karat scale.
Modern use
Modern use is context-dependent and varies by region or measurement system.