Understanding ISO Cleanliness Codes

The ISO cleanliness codes are derived from International Standard ISO 4406:2017. 

ISO codes show 3 sets of separated numbers. These numbers refer to ranges depicting the number of particles 'larger than' 4 micron, 6 micron and 14 micron per 1mL respectively. Obviously, as 6 micron and 14 micron particles are both larger than 4 micron, those particles are all also present in the first number. The second number only shows particles larger than 6 micron. The last number only shows particles larger than 14 micron.

The table below shows the number of particles in 100mL of fluid that is specified against each number in the range. Based on the example shown, there are literally millions of small particles present in just 100mL of fuel or oil at a cleanliness level of ISO 22/21/18.



ISO 4406 CONTAMINATION CODES

Range of number of particles per 100 milliliters 

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

Common Industry ISO Cleanliness Ratings

ISO 22/21/18 - Common cleanliness level of fluids. ISO 18/16/13 - Target rating for heavy gear/engine oils. ISO 16/14/11 - Target rating for hydraulic/transmission oils. ISO 14/13/11 - Target rating for diesel fuel.

Did You Know?

A 120 lpm pump working 8 hours a day using fluid that is ISO 18/16/13 will pass 9 kgs of dirt in 200 days.