Cleanroom Classification Calculator
Calculate particle count limits by ISO 14644-1 cleanroom class with EU GMP grade mapping.
About this calculator
ISO 14644-1:2015 defines cleanroom cleanliness classes with one deceptively simple formula: Cn = 10^N × (0.1/D)^2.08, where N is the ISO class number and D is the particle diameter in micrometers being measured against. This calculator plugs your chosen class and particle size straight into that formula to get the maximum allowable particle count per cubic meter, and separately computes the limits at the two sizes most commonly cited in specs (0.5 µm and 5.0 µm) so you can see both at once. It also converts the result to particles per cubic foot for cross-reference against the older US Fed Std 209E system, which used cubic-foot counts before being superseded by ISO 14644.
A rough required-airflow figure comes from your room volume times air changes per hour, converted to CFM — a planning number for HVAC sizing, not a substitute for actual airflow validation. If you enter a measured particle count, the calculator checks it against the class limit and reports a compliance margin (positive means you're under the limit and passing). The EU GMP grade mapping is only an approximate cross-reference: Grade A/B environments correspond to ISO 5, Grade C sits between ISO 7 and 8, and Grade D to ISO 8, but GMP grading also distinguishes "at rest" from "in operation" states in ways a single ISO class number doesn't capture — always confirm against the actual EU GMP Annex 1 table for regulatory submissions rather than relying on this mapping alone.
Inputs
Results
Max particles/m³
351,676
Figures current as of 2015. Source: ISO 14644-1:2015, "Cleanrooms and associated controlled environments — Part 1: Classification of air cleanliness by particle concentration," International Organization for Standardization
How to Use This Calculator
- Select your ISO class (1–9) and the particle size threshold (µm) to evaluate.
- Enter room volume (m³) and your HVAC air changes per hour.
- Optionally enter a measured particle count per m³ to check compliance.
- Review Max Particles/m³, Required Airflow (CFM), and Compliance Margin (%).
- A positive compliance margin confirms your room is within the ISO class limit.
How the result changes with ISO class (1-9)
| ISO class (1-9) | Max particles/m³ |
|---|---|
| 3.5 | 352 |
| 5.25 | 3,517 |
| 9 | 35,167,572 |
What each input means
- ISO class (1-9)
- ISO 14644-1 class number. Biotech: ISO 5 (aseptic), ISO 7 (controlled), ISO 8 (general).
- Particle size (µm)
- Particle diameter threshold in micrometers. Common: 0.5 µm and 5.0 µm.
- Room volume (m³)
- Cleanroom volume in cubic meters for airflow calculations.
- Air changes per hour
- HVAC air changes per hour. ISO 5: 240-600, ISO 7: 60-90, ISO 8: 10-25.
- Measured particle count (/m³)
- Your measured particle count per m³ (enter 0 to skip compliance check).
What each result means
- Max particles/m³
- Maximum allowable particles per cubic meter at specified size for this ISO class.
- Max particles/ft³
- Equivalent limit per cubic foot (Fed Std 209E reference).
- Limit at 0.5 µm (/m³)
- Max particles ≥0.5 µm per m³ for this ISO class.
- Limit at 5.0 µm (/m³)
- Max particles ≥5.0 µm per m³ for this ISO class.
- Required airflow (CFM)
- Air volume flow rate in cubic feet per minute.
- Compliance margin (%)
- Margin between your measurement and the class limit. Positive = pass.
- Passes spec (1=yes, 0=no)
- Whether your measured count is within the ISO class limit.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersISO class (1-9) = 7, Particle size (µm) = 0.5, Room volume (m³) = 100, Air changes per hour = 20 = 5 input(s) provided
- Calculate Max particles/m³Max particles/m³ = pow(10, isoClass) * pow(0.1 / particleSizeUm, 2.08)351676 = 351676
- Calculate Max particles/ft³Max particles/ft³ = maxParticlesPerM3 / 35.31479958 = 9958
- Calculate Limit at 0.5 µmLimit at 0.5 µm = pow(10, isoClass) * pow(0.1 / 0.5, 2.08)351676 = 351676
Figures and sources
- ISO 14644-1:2015 particle concentration classification formula (Cn = 10^N × (0.1/D)^2.08) (2015) — ISO 14644-1:2015, "Cleanrooms and associated controlled environments — Part 1: Classification of air cleanliness by particle concentration," International Organization for Standardization
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does the particle limit change so much between 0.5 µm and 5.0 µm at the same ISO class?
The ISO 14644-1 formula, Cn = 10^N × (0.1/D)^2.08, has particle diameter D raised to a negative power close to 2, so smaller particle sizes give a much larger allowable count. At ISO class 7, for example, the 0.5 µm limit is far higher than the 5.0 µm limit because the exponent makes the count drop off steeply as the size threshold increases.
Why does entering a lower ISO class number produce a stricter particle limit?
The class number N sits directly in the exponent as 10^N, so each step down in ISO class multiplies the maximum allowed particle count by 10. ISO 5 permits far fewer particles per cubic meter than ISO 8, which is why lower classes are used for aseptic filling and higher classes for general controlled areas.
Is the EU GMP grade shown here a precise regulatory classification?
No — it's an approximate cross-reference mapping ISO class ranges to GMP letter grades (for example, ISO 7 in operation maps loosely to Grade C), used only for at-a-glance orientation. EU GMP Annex 1 distinguishes 'at rest' from 'in operation' particle limits separately for each grade, a distinction a single ISO class number can't fully capture, so a regulatory submission should reference the actual Annex 1 table rather than this mapping.
How is the required airflow (CFM) figure calculated, and is it enough to size an HVAC system?
It's simply room volume times air changes per hour, converted from m³/hr to cubic feet per minute using the 35.3147 ft³/m³ conversion factor — a planning-level number only. It doesn't account for filtration efficiency, room leakage, equipment heat load, or actual airflow uniformity, so real HVAC sizing still needs proper engineering design and airflow validation testing.
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