| Particle size (µm) | Measured count (per m³) | Typical interpretation |
|---|---|---|
| 0.3 | 3,500,000 | Higher counts often drive the class upward. |
| 0.5 | 352,000 | Common reference size for many facilities. |
| 1.0 | 83,200 | Useful for tracking filtration performance shifts. |
| 5.0 | 2,930 | Often lower, but still relevant to compliance. |
This calculator uses the ISO 14644-1 particle concentration relationship: Cn = 10^N × (0.1 / D)2.08
- Cn = maximum allowed particle concentration (particles per m³)
- N = ISO class number
- D = particle size (µm)
To estimate the class from a measured concentration, the rearranged form is used: N = log10(Cn) + 2.08 × log10(D / 0.1).
- Select the unit that matches your particle counter output.
- Enter a target ISO class for pass/fail comparison.
- Input measured particle counts at one or more sizes.
- Choose conservative rounding for reporting and audits.
- Press calculate, then download CSV or PDF reports.
ISO class as a construction acceptance metric
Cleanroom performance is verified by particle concentration at defined sizes and locations. During fit‑out and commissioning, class targets confirm envelope integrity, finishes, and HVAC stability. A single high count at a critical size can raise the estimated class and trigger corrective work. HEPA filters are often specified at 99.97% efficiency at 0.3 µm, so abnormal trends may indicate bypass leakage.
How the calculator turns counts into class
The calculator applies the ISO relationship Cn = 10^N × (0.1/D)^2.08, where D is particle size in µm and Cn is particles per m³. From measured concentration, it uses N = log10(Cn) + 2.08×log10(D/0.1). Rounding options let you report conservatively (ceiling) or for internal diagnostics (nearest).
Input structure, units, and sampling notes
Particle counters may report per ft³ or per m³. This tool converts per ft³ to per m³ using 1 m³ = 35.3147 ft³. Enter any subset of common sizes (0.1, 0.2, 0.3, 0.5, 1.0, 5.0 µm) plus a custom size. Zero values are treated as not measured. Keep sample volume, duration, and location consistent between runs.
Using results to steer installation decisions
Worst‑case evaluation summarizes multiple sizes conservatively, while single‑size mode aligns with a project specification. Compare each row against the target class to see which size drives nonconformance. Larger‑size failures point to housekeeping, material handling, or door discipline; smaller‑size failures suggest filter integrity, leakage paths, or airflow balance. Many projects also track pressure differentials, commonly 5–15 Pa between adjacent zones. Include temperature and humidity at test time to explain short-term variability.
Exports for QA/QC documentation
CSV export supports trending across rooms, dates, and contractors. The PDF report provides a compact snapshot for handover packages, method statements, and commissioning sign‑offs. Record the instrument model, calibration date, sample volume, and test map alongside exported results to maintain traceability during client audits.
Which ISO classes can I evaluate?
Enter target classes from ISO 1 to ISO 9. The tool estimates an overall class from your measurements and compares each size against the selected target for a quick PASS/FAIL screen.
Can I use counts reported per cubic foot?
Yes. Choose the per ft³ option and enter counts exactly as displayed by your counter. The calculator converts to per m³ internally using 1 m³ = 35.3147 ft³, then applies the ISO equation.
Why might I see PASS by rows but a higher overall class?
Row checks compare measured counts to the target’s allowable limits at each size. The overall estimate uses your rounding choice and worst-case logic, which can be more conservative than a single-row comparison.
Does this replace formal ISO 14644 classification testing?
No. It is a planning and documentation aid. Formal classification requires defined sampling locations, sample volume rules, and statistical criteria, plus controlled operating states and calibrated instrumentation.
What sizes should I enter for typical projects?
Use the sizes required by your specification or customer standard. Common reporting includes 0.5 µm and 5.0 µm, while smaller sizes such as 0.3 µm help diagnose filtration and leakage issues earlier.
How should I treat zero counts or missing sizes?
Leave fields blank or enter zero for sizes you did not measure or that were below detection. The calculator skips non-positive values, so provide at least one positive count to generate an estimate.