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Clean Rooms - ISO Standard 14644

Clean room class limits according ISO Standard 14644-1.

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Clean rooms maintained virtually free of contaminants, such as dust or bacteria, are used in laboratory work and in the production of precision parts for electronics or aerospace equipment.

In the clean room standard ISO 14644-1 "Classification of Air Cleanliness" - the classes are based on the equation

Cn = 10N (0.1 / D)2.08                                     (1)


Cn = maximum permitted number of particles per cubic meter equal to or greater than the specified particle size, rounded to whole number

N = ISO class number - must be a multiple of 0.1 and be 9 or less

D = particle size in micrometers

Maximum Number of Particles in Air
(particles in each cubic meter equal to or greater than the specified size)
Particle size
> 0.1 μm> 0.2 μm> 0.3 μm> 0.5 μm> 1 μm> 5 μm
ISO Class 1 10 2
ISO Class 2 100 24 10


ISO Class 3 1000 237 102 35 8
ISO Class 4 10000 2370 1020 352 83
ISO Class 5 100000 23700 10200 3520 832 29
ISO Class 6 1000000 237000 102000 35200 8320 293
ISO Class 7 352000 83200 2930
ISO Class 8 3520000 832000 29300
ISO Class 9 35200000 8320000 293000

clean room particles sizes iso standard diagram

ISO Clean room Standards

  • ISO-14644-1 Classification of Air Cleanliness
  • ISO-14644-2 Clean room Testing for Compliance
  • ISO-14644-3 Methods for Evaluating & Measuring Clean rooms & Associated Controlled Environment
  • ISO-14644-4 Clean room Design & Construction
  • ISO-14644-5 Clean room Operations
  • ISO-14644-6 Terms, Definitions & Units
  • ISO-14644-7 Enhanced Clean Devices
  • ISO-14644-8 Molecular Contamination
  • ISO-14698-1 Biocontamination: Control General Principles
  • ISO-14698-2 Biocontamination: Evaluation & Interpretation of Data
  • ISO-14698-3 Biocontamination: Methodology for Measuring Efficiency of Cleaning Inert Surfaces
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  • Engineering ToolBox, (2005). Clean Rooms - ISO Standard 14644. [online] Available at: [Accessed Day Mo. Year].

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