Understanding ISO Cleanliness Codes

ISO Cleanliness Code is a three digit value used to communicate particulate contamination in oil. The international standard for reporting contamination is ISO 4406:99. A laser is used to count particles of various sizes, within a 1 ml sample, and reported in three channels.

The first number represents the total quantity of particles >4 microns. The second number represents the total quantity of particles >6 microns. The third number represents the total quantity of particles >14 microns.

The table below is a common representation of ISO Cleanliness Codes.  Notice as the ISO Code number increases by one the quantity range doubles.  In other words, an ISO Code of 11 communicates a range of particles between 10 to 20 in number.  An ISO Code of 12 communicates a range of particles of 20 to 40 in number.  


ISO Cleanliness Code Table

When applied to filtration, a common oil cleanliness goal is ISO 16/13/11.  This mean that in a 1 ml sample, the laser counted between 320-640 particles 4 micron and greater; between 40-60 particles 6 micron and greater and 10-20 particles 14 micron and greater.

Below is a typical oil analysis report reporting oil cleanliness.  The first column (bold) reports an ISO Cleanliness Code of 19/13/10.  The first number, “19”, is reporting the 4,134 particles >4 micron.  The second number, “13” is reporting the 72 particles >6 micron and the third number, “10” is reporting the 2 particles >14 micron counted. 

Assuming for a moment that the sample was taken correctly and our cleanliness goal is 16/13/11, we would have some investigating to do. We need to look at our current level of filtration. We may consider replacing with tighter media or adding offline filtration.

In the near future we will discuss particle counters and options available.