What is ISO 4406?

ISO 4406 is the international standard for classifying the cleanliness level of oil used in hydraulic and lubrication systems. It uses a three-number code representing the concentration of solid particles at different sizes, providing a universal language for specifying and measuring fluid cleanliness.

Understanding the Cleanliness Code

An ISO 4406 code like 18/16/13 breaks down as:

First number: Scale number for particles ≥4μm per milliliter
Second number: Scale number for particles ≥6μm per milliliter
Third number: Scale number for particles ≥14μm per milliliter

The lower the number, the cleaner the fluid.

Cleanliness Requirements by Industry

Application	Recommended ISO 4406
Aerospace hydraulics	13/11/8 or better
Precision servo hydraulics	15/13/10
Industrial hydraulics	18/16/13
Gearbox lubrication	19/17/14
Engine lubricating oil	20/18/15

How to Measure Cleanliness

Particle counters like the LUWATECH LWB-6 and LWL-3 series directly measure particle distribution in oil samples and automatically calculate the ISO 4406 code. Portable units are ideal for field testing; online units enable 24/7 continuous monitoring.

Recommended LUWATECH Products

Field testing: LWB-6 Portable Particle Counter
Online monitoring: LWL-3 Online Particle Counter
Lab analysis: LWT-2A Desktop Particle Counter

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