ISO 4406:1999 Standard for Oil

ISO 4406:1999 is the internationally recognised method of quoting the solid particulate count in oil. It is also referred to as the ISO cleanliness code. When an oil is tested against ISO standards it will be given a rating in 3 numbers. For a hydraulic oil to be considered ‘clean’ a rating of 18/15/12 is considered to be acceptable.

What does “18/15/12” mean?

The cleanliness code identifies the number of particles that are present in 100 ml of fluid. For the code quoted above:

  • The first number (18) indicates the level of contamination by particles greater than 4 micron
  • The second number (15) indicates the level of contamination by particles greater than 6 micron
  • The third number (12) indicates the level of contamination by particles greater than 14 micron

For the example given above (18/15/12) the following table shows what each of the range number translates to in terms of particle quantities:

Range Number Micron Size Particle Count Range
18 4+ 1300 – 2500
16 6+ 320 – 640
13 14+ 40 – 80

To give you an idea of scale in terms microns:

  • Bacteria is 10 micron
  • A human hair is 70 micron
  • A grain of salt is 100 micron
  • The naked eye can detect particles over 40 micron

 

ISO 4406 Cleanliness Table

The table below is an extension of the example given above. It translates what each ISO ‘range number’ means in terms of number of particles found at each micron test.

Range Number Particle Count Range
>28 2,500,001+
28 2,500,000 – 1,300,001
27 1,300,000 – 640,001
26 640,000 – 320,001
25 320,000 – 160,001
24 160,000 – 80,001
23 80,000 – 40,001
22 40,000 – 20,001
21 20,000 – 10,001
20 10,000 – 5,001
19 5,000  – 2,501
18 2,500 – 1,301
17 1,300 – 641
16 640 – 321
15 320 – 161
14 160 – 81
13 80 – 41
12 40 – 21
11 20 – 11
10 10 – 6
9 5 – 2.6
8 2.5 – 1.4
7 1.3 – 0.65
6 0.64 – 0.33
5 0.32 – 0.17
4 0.16 – 0.09
3 0.08 – 0.05
2 0.04 – 0.03
1 0.02 – 0.02
0 0.01 – 0

 

For more information on ISO 4406:1999

Detailed Information on ISO 4406:1999 is not available free-of-charge. It has to be purchased from the International Organization for Standardization (ISO) website. The full text of the standard can be purchased from the ISO Website. For this reason, it cannot be made available for download from IPU’s web site.