Understanding the cleanliness of your fluid is the first step in any contamination control program. While other systems are also used to measure the cleanliness of fluids, ISO cleanliness codes are commonly utilised globally. Derived from ISO 4406:2017, these codes quantify the level of particle contamination in oils and fuels. While ISO 4406 provides no understanding of the types of contamination in your fluid, it does provide the quantity of particulates in your fluid.
What Are ISO Cleanliness Codes?
An ISO cleanliness code provides a number like 22/21/18. Unless you work with ISO codes every day, the numbers mean little without the chart. Each number of the 3-digit code represents a quantity range of particles at a given particle size in a fluid sample. ISO 4406 counts particle sizes of:
- 4 microns and larger
- 6 microns and larger
- 14 microns and larger
- The first number ??/--/-- refers to all particles 4 microns and larger.
- The second number --/??/-- refers to all particles 6 microns and larger
- The third number --/--/?? refers to all particles 14 microns and larger
The chart below refers to ranges of particle counts in 100 mL of fluid. Please note that some organisations provide counts per 1mL of fluid, and while the data tells the same story, the particle ranges on their charts will be 1/100th of the chart below.
Code |
More Than |
Up to & Including |
24 |
8,000,000 |
16,000,000 |
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 |
To put it in perspective, a code of 22/21/18 means that in a 100mL sample bottle, expect:
- Between 2,000,000 and 4,000,000 particles 4 microns and larger
- Between 1,000,000 and 2,000,000 particles 6 microns and larger
- Between 130,000 and 250,000 particles 14 microns and larger
Please note:
Why It Matters
Even though fuel or oil may look clean, contamination at the microscopic level can cause serious wear and system damage. ISO cleanliness codes help:
- Quantify contamination levels
- Track fluid cleanliness over time
- Set filtration goals and cleanliness targets
- Initiate a contamination control program
Keep Your System Clean with the Right Filtration
Understanding your fluid’s ISO code helps you select the right filters for your system. Lower ISO codes mean cleaner fluid and longer equipment life.
At Donaldson, we provide advanced filtration solutions tailored to meet or exceed your required ISO cleanliness levels. Our filters help keep your equipment running smoothly, with less downtime and reduced maintenance costs.
