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Fuel Filtration: ISO 4406 Basics

An ISO-4406 cleanliness rating for fluids is expressed as three numbers. Here's what they mean

August 13, 2015

An ISO-4406 cleanliness rating for fluids is expressed as three numbers, such as 17/15/10. The numbers, left to right, are codes for the approximate number of particles— contained in a very small (1-milliliter) sample—that are 4 microns and larger, 6 microns and larger, and 14 microns and larger. A 17 code in the example indicates that the 1-milliliter sample likely contains between 640 and 1,300 particles 4 microns and larger.

The ISO system actually is based on analyzing 100-milliter (about 4-ounce) samples with a particle-counting instrument to determine the number of particles present in each of the three size ranges. The code numbers and their associated particle counts are a function of the number 2 being multiplied by itself. A 10 code in the example means that 210 or 1,024 particles 14 microns and larger were in the sample.

Each code actually represents a range of particle counts, so a 10 means that the 100-milliliter sample contains between 29 (512) and 210 (1,024) particles. Since the ISO system is based on particles/milliliter, however, those counts are divided by 100, meaning that a 10 code represents a 1-milliliter sample with between 5 and 10 particles in a given size range. The ISO-4406 chart rounds particle counts in some instances for convenience.

Code Particles/100 ml Particles/ml
6 64 0.32-0.64
7 128 0.64-1.3
8 256 1.3-2.5
9 512 2.5-5
10 1,024 5-10
11 2,048 10-20
12 4,096 20-40
13 8,192 40-80
14 16,384 80-160
15 32,768 160-320
16 65,536 320-640
17 131,072 640-1,300
18 262,144 1,300-2,500
19 524,288 2,500-5,000
20 1,048,576 5,000-10,000
21 2,097,152 10,000-20,000
22 4,194,304 20,000-40,000
23 8,388,608 40,000-80,000
24 16,777,216 80,000-160,000

 

 

 

 

 

 

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