ISO Cleanliness Code

Canonical Definition

A three-number code defined by ISO 4406 that quantifies the particle contamination level in a fluid sample. Each number represents the quantity of particles per millilitre in a specific size range: the first covers particles ≥4 µm(c), the second ≥6 µm(c), and the third ≥14 µm(c). Each code number represents a particle count range in powers of two — code 16 = 320–640 particles/mL, code 14 = 80–160 particles/mL. A cleanliness code of 16/14/11 means: 320–640 particles ≥4 µm, 80–160 particles ≥6 µm, and 10–20 particles ≥14 µm per millilitre. Tighter codes (lower numbers) indicate cleaner fluid and reduce risk of abrasive wear, valve stiction, and bearing failure.

Engineering Context

ISO cleanliness codes are the global standard for specifying and verifying hydraulic and lubrication system fluid cleanliness. Target codes vary by component sensitivity: servo valves require 15/13/10 or tighter; general hydraulic systems typically target 17/15/12; engine lube systems target 16/14/11. Cleanliness codes are measured by laser particle counting per ISO 11171.

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