ISO Cleanliness Codes
Wednesday, July 29, 2020
Why is clean oil important?
Clean oil decreases the lifetime operating expense of a piece of equipment, which maximizes the lifetime usefulness and produces a greater return on investment. ISO Cleanliness codes are the way the lubricants industry describes the cleanliness of an oil and were established from the International Standard ISO 4406-99.
An ISO code is a set of three numbers separated by slash marks that refers to the number of particles of certain sizes in 100 milliliters of a fuel or oil. Since there are so many particles in that sample size, the designation is a range of numbers such as "greater than 2 million but less than 4 million." The different numbers refer to the size of the particles in microns or micrometers (μm) and are listed in the order below:
- The number of particles greater than 4 μm
- The number of particles greater than 6 μm
- The number of particles greater than 14 μm
The chart at the end of this article can be used as a reference to help determine what a reported ISO cleanliness code really means.
For example, if a fuel or oil has a cleanliness level of ISO 22/21/18 we can use the chart to see the corresponding number of particles in each micron size that are present in 100 milliliters of the fluid.
| 22 |
21 |
18 |
|
Between 2 million and 4 million particles
4 micron or larger
|
Between 1 million and 2 million particles
6 micron or larger
|
Between 130,000 and 250,000 particles
14 micron or larger
|
Some equipment manufacturers will only use two of the three designations, such as ISO 21/18, if particles as small as 4 microns are not a concern.
ISO Cleanliness Standards (number of particles per 100 mL)
| Range no. |
More than |
Up to and including |
| 24 |
8,000,000 |
18,000,000 |
| 23 |
4,000,000 |
8,000,000 |
| 22 |
2,000,000 |
4,000,000 |
| 21 |
1,000,000 |
2,000,000 |
| 20 |
500,000 |
1,000,000 |
| 19 |
250,000 |
500,000 |
| 18 |
130,000 |
250,000 |
| 17 |
64,000 |
130,000 |
| 16 |
32,000 |
64,000 |
| 15 |
16,000 |
32,000 |
| 14 |
8,000 |
16,000 |
| 13 |
4,000 |
8,000 |
| 12 |
2,000 |
4,000 |
| 11 |
1,000 |
2,000 |
| 10 |
500 |
1,000 |
| 9 |
250 |
500 |
| 8 |
130 |
250 |
| 7 |
64 |
130 |
| 6 |
32 |
64 |
| 5 |
16 |
32 |
| 4 |
8 |
16 |
| 3 |
4 |
8 |
| 2 |
2 |
4 |
| 1 |
1 |
2 |
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