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ISO Cleanliness Codes Explained

ISO cleanliness codes are based on International Standard ISO 4406:99. ISO codes show three sets of numbers separated by a slash. These numbers refer to ranges depicting the number of particles larger than 4 micron, 6 micron and 14 micron respectively. Because 6 micron and 14 micron particles are both larger than 4 micron those particles are all also included in the first number. The second number shows particles larger than 6 microns. The last number only shows particles larger than 14 microns.

The table indicates the number of particles in 100mL of fluid that is specified against each number in the range.

ISO 4406 Cleanliness Standards

(number of particles per 100 mL)*

Range no.More thanUp to and including
248,000,00018,000,000
234,000,0008,000,000
222,000,0004,000,000
211,000,0002,000,000
20500,0001,000,000
19250,000500,000
18130,000250,000
1764,000130,000
1632,00064,000
1516,00032,000
148,00016,000
134,0008,000
122,0004,000
111,0002,000
105001,000
9250500
8130250
764130
63264
51632
4816
348
224
112
Example:

A dirty hydraulic oil could have an ISO cleanliness level of 22/20/18.

ISO 22/20/18
particles sizenumber of particlesrange no.
4µm +2,000,000 ≤ 4,000,00022
6µm +500,000 ≤ 1,000,00020
14µm +130,000 ≤ 250,00018
*Note: ISO 4406 states particles per 1mL