ISO 21501-4 – Particle Counter Calibration

Learn more about requirements for ISO 21501-4

Single particle light interaction methods

ISO 14644-1:2015 introduces the need for particle counters calibrated to ISO 21501-4. The calibration methods assure data accuracy and repeatability. The methods outlined in ISO 14644 and ISO 21501-4 represent an important step in a more accurate evaluation of cleanroom contamination and improved process control.


ISO 21501: 2018 Determination of particle size distribution—Single particle light interaction methods – Part 4: Light scattering airborne particle counter for clean spaces

The documentation and approval of ISO 2151-4:2007 subsequently replaces and cancels ISO 13323- 1:2000. The ISO 21501 standard widens the scope of analysis to include the methodology for airborne particle counting and liquid particle counting (both light scattering and extinction methods). Specifically, ISO 21501-4 provides a calibration procedure and verification method for airborne particle counters to minimize inaccurate measurements and reduce variations between different instruments. These new guidelines require pulse height analysis (PHA) for particle counter calibrations, which reduces inconsistencies.

Read this comprehensive paper titled Understanding ISO 21501-4 for Life Sciences Industries from Particle Measuring Systems that lists all  ISO 21501-4 calibration requirements and a description of the test method adopted.


PMS Worldwide local particle counter calibration services include:

  • Particle counter calibration and verification/validation and adjustments back to factory standards
  • Calibration certificate issued with each instrument
  • Preventative maintenance
  • Technical Support:
  • Software Support:
  • Instrument examination (as found and as left data available)
  • NIST traceable


Learn more about our Worldwide local Service and calibration centers.
Contact us today for a quote


Understanding ISO 21501-4 Particle Counter Calibration

ISO 21501-4 has two main goals: 1) to improve instrument-to-instrument (particle counter) data correlation and count accuracy, and 2) to enhance compliance with ISO 14644. By the end of this webinar, you will have a good understanding of the following concepts and how they affect your cleanroom particle counting efforts:

  • How to be compliant with the most recent particle counter calibration requirements
  • Particle counter resolution and counting efficiency
  • False count rate
  • Particle size setting
  • Coincidence loss at maximum particle concentration

Learn More


Contamination Control Products

Portable Particle Counter: Lasair® Pro

Learn More
Handheld Particle Counter: Handilaz® Mini II

Learn More
Airnet® II / IIs Remote Air Particle Counter (2 Channels)

Learn More
Remote Particle Counter: IsoAir® Pro

Learn More

Or, let us help you find a solution for your contamination monitoring:

Still have Questions?

Our customer support is ready to answer your questions or get a quote ready for you.

Contact Customer Support Contact Service