# Which Particle Counter Device for the Sampling Record at Data Center?

> When selecting a particle counter device for taking sampling records in a data center to comply with ISO 14644-1 standards, it is crucial to use a device that meets specific performance requirements.

- Author: Ashraf Almuhtaseb (Data Center Cleaning Specialist)
- Published: 2026-06-06
- Updated: 2026-11-05
- URL: https://idata.center/en/articles/choosing-particle-counter

## Key takeaways

- Data hall ISO 14644-1 tests require a light-scattering particle counter calibrated to ISO 21501-4 with 0.5 um and 5 um channels.
- The counter must include a valid ISO 21501-4 calibration certificate that remains in date on the day of the test.
- Handheld counters typically sample at 2.83 L/min, while larger portable units use 28.3 L/min, both meeting the 2-liter minimum.
- Portable or handheld counters are practical for data halls to navigate narrow aisles and sample at server-intake height.

## Which Particle Counter Should You Use for an ISO 14644-1 Test?

 

For an ISO 14644-1 test in a data hall, you need a light-scattering airborne particle counter calibrated to ISO 21501-4, with channels at 0.5 µm and 5 µm. A data hall is normally classified at ISO Class 8, and those are the two sizes that class is checked at.

 

Everything else on the data sheet, from screen size to the number of channels, is a matter of convenience. Get the calibration and the channels right first.

 

## Why does ISO 21501-4 calibration matter?

 

[ISO 21501-4](https://www.iso.org/standard/58073.html) sets how a light-scattering particle counter for clean spaces is calibrated and checked: size setting, counting efficiency, sample flow rate and false counts, among other points. [ISO 14644-1:2015](https://www.iso.org/standard/53394.html) refers to it for the instruments used in classification.

 

In practice this means two things for you:

 

- The counter must come with a valid ISO 21501-4 calibration certificate, issued by the maker or an accredited lab.
- The certificate must still be in date on the day of the test. Attach a copy to every test report.

 

**Note:** The typical recalibration interval is once a year; ensure that the manufacturer has a local branch or that there is an accredited laboratory available to perform annual recalibration.

 

## Which particle sizes do you need?

 

ISO Class 8 sets limits at 0.5 µm, 1 µm and 5 µm. You choose the sizes for classification with your client, and in data centers the usual pair is 0.5 µm and 5 µm.

 

| Size channel | Needed for ISO Class 8? | What it tells you |
| --- | --- | --- |
| 0.3 µm | No | Useful for checking filter performance |
| 0.5 µm | Yes | Main classification size |
| 1.0 µm | Optional | Extra detail between the two main sizes |
| 5.0 µm | Yes, usually | Larger dust, the fraction that settles on equipment |

 

The old belief that a data center test must include 0.3 µm comes from cleanroom work at stricter classes. It does no harm to have the channel, but it is not a requirement. If you need a refresher on the sizes, see [what µm means](https://idata.center/en/articles/micrometer-particle-size).

 

Also remember that the counts are cumulative. The figure on the 0.5 µm channel means "particles of 0.5 µm and larger", so it includes the 1 µm and 5 µm particles too.

 

## What flow rate should the counter have?

 

The standard does not fix a flow rate. It fixes a minimum of 2 litres of air and 1 minute of sampling at every location. Handheld counters commonly sample at 2.83 L/min (0.1 CFM), and larger portable units at 28.3 L/min (1 CFM).

 

**Note: confirm the flow rate of the counter you use.**

 

Both meet the minimum in one minute. The higher flow rate gives you more counts per minute at 5 µm, which makes the result at that size more stable. The lower flow rate gives you a lighter instrument that you can carry from rack to rack all day.

 

How many locations you need is set by the room area. The calculation is in [number of sample locations for ISO 14644-1](https://idata.center/en/articles/iso-14644-sampling-locations).

 

## Portable or handheld?

 

For data halls, a handheld or small portable counter is the practical choice. You will move between dozens of points, often in narrow aisles and between hot and cold containment.

 

Look for:

 

- An isokinetic probe and a small tripod or stand, so you can sample at server-intake height without holding the unit.
- A battery that lasts a full test day, or a spare battery.
- A purge filter, so you can run a zero count before you start.

 

## Data logging and the test report

 

A certificate is only as good as its raw data. Choose a counter that stores every sample with its location number, date, time and sample volume, and that exports to a spreadsheet or PDF without retyping.

 

Before each job:

 

1. Check the calibration certificate date.
2. Run a zero count with the purge filter fitted.
3. Set the sample time to at least one minute and the sizes to the ones agreed with the client.
4. Name each location to match the numbers on your floor plan.

 

After the job, keep the raw export with the report. If a client or auditor questions a result, you can show the original record rather than a summary.

 

## Before you buy

 

Ask the supplier for the ISO 21501-4 certificate and a sample report before you pay. If they cannot show both, the counter is not suitable for classification work, however good the price.

 

The timing of the test after cleaning is covered in [when to take the ISO 14644 reading](https://idata.center/en/articles/iso-14644-test-timing), and the class limits in [ISO 14644 cleanroom classes](https://idata.center/en/articles/iso-14644-cleanroom-classes).

 

A calibrated counter with the right channels and clean records will serve you for years. A cheaper unit without a certificate gives you numbers no one can rely on.

## Frequently asked questions

### What type of particle counter is required for an ISO 14644-1 test in a data hall?

You need a light-scattering airborne particle counter calibrated to ISO 21501-4. It must have channels at 0.5 µm and 5 µm to meet the requirements for ISO Class 8 classification.

### Why is an ISO 21501-4 calibration certificate necessary?

ISO 14644-1:2015 requires instruments used in classification to be calibrated according to ISO 21501-4. You must have a valid, in-date certificate from the manufacturer or an accredited lab to attach to every test report.

### What flow rate should the particle counter have?

The standard does not mandate a specific flow rate, provided you sample at least 2 litres of air for 1 minute at every location. Both 2.83 L/min and 28.3 L/min flow rates meet this requirement.

### Is it necessary to include a 0.3 µm channel for data center testing?

No, a 0.3 µm channel is not a requirement for ISO Class 8 classification. While it does no harm to have it, the main classification sizes for a data center are 0.5 µm and 5 µm.

### What features should I look for when choosing a particle counter for a data hall?

Choose a handheld or portable unit with an isokinetic probe, a tripod, and a battery that lasts a full day. It should also include a purge filter and the ability to store and export raw data with location, date, time, and volume details.

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Ashraf Almuhtaseb is a Data Center Technical Cleaning Expert with over 9 years of specialized field experience since 2017, and the only independent professional in the MENA region publishing dedicated technical content on data center cleaning, contamination control, and ISO 14644 compliance.

© 2026 Ashraf Almuhtaseb — https://idata.center/