ISO 4406Understanding the ISO 4406:1999 Cleanliness Guide

The currently standard for measuring particulate in oils is the standard from ISO 4406:1999 but can be a little difficult to understand. So here is our attempt to simplify it for you:

Essentially ISO 4406:1999 represents a standardised method of counting and reporting the number of particles of contamination found in an oil. The most common method of counting particles today is to pump the oil past a fine laser beam. The laser looks for particles that are 4µm, 6µm & 14µm (4,6 & 14 microns) and generates a total number of particles over a set time for each size. This can then be referenced back to the ISO Standard Table as shown below to produce a Cleanliness Code. Lower the numbers in the code represents fewer particles in the oil. Examples of codes and their corresponding applications are:


 

For example: The industry standard code for diesel used in engines is 18/16/13.

  • 18 = More than 1300 and up to 2500 particles larger than 4µm exist in the sample.
  • 16 = More than 320 and up to 640 particles larger than 6µm exist in the sample.
  • 13 = More than 40 and up to 80 particles larger than 14µm exist in the sample.

 

Number of Particles per mL Typical Applications
4µm 6µm 14µm
14 12 9 High precision & laboratory servos
17 15 11 Robotic & servo systems
18 16 13 Very sensitive & high reliability systems
20 18 14 Sensitive & reliable systems
21 19 16 General equipment of limited reliability
23 21 18 Low pressure equipment – not much use

 

Number of Particles per mL
More than Up to and Including Scale No.
2.5M > 28
1.3M 2.5M 28
640k  1.3M 27
 320k 640k 26
 160k 320k 25
80k 160k 24
40k 80k 23
20k 40k 22
10k 20k 21
5000 10k 20
2500 5000 19
1300 2500 18
640 1300 17
320 640 16
160 320 15
80 160 14
40 80 13
20 40 12
10 20 11
5 10  10
2.5 5 9
1.3 2.5 8
0.64 1.3 7
0.32 0.64 6
0.16 0.32 5
0.08 0.16 4
0.04 0.08 3
0.02 0.04 2
0.01 0.02 1
0.0 0.01 0

 

This code has been superseded by ISO 4406:2017