Cleanroom Classification

Prepared and reviewed by the PrepElephant Academic Review Team

First published 2 Oct 2026 · Spot an error?

On this page

Direct answer
What you must remember
Classifying a room in practice
Where students slip
Frequently asked questions
Related topics

Direct answer

Cleanrooms are classified by the concentration of airborne particles per cubic metre, standardised in ISO 14644-1:2015: ISO Class 5 permits 3,520 particles of 0.5 micrometre and larger per cubic metre, ISO 6 permits 35,200, ISO 7 permits 352,000 and ISO 8 permits 3,520,000 — limits pharmaceutical GMP overlays with its Grade A to D system. In EU GMP and WHO guidance, and now in India's revised Schedule M, Grade A equals ISO 5 in operation, Grade B is ISO 5 at rest degrading to ISO 7 in operation, Grade C is ISO 7 at rest falling to ISO 8 in operation, and Grade D is ISO 8 at rest. Classification is always stated with its occupancy state — as-built, at-rest or in-operation — because people generate most particles, with requalification every six months for ISO 5 and better and annually for the rest.

What you must remember

Core ISO numbers at 0.5 micrometre: ISO 5 = 3,520; ISO 6 = 35,200; ISO 7 = 352,000; ISO 8 = 3,520,000 particles per cubic metre — ten-fold steps that make the table easy to reconstruct under exam pressure.
Grade mapping: Grade A ISO 5 in operation; Grade B ISO 5 at rest and ISO 7 in operation; Grade C ISO 7 at rest and ISO 8 in operation; Grade D ISO 8 at rest (no formal in-operation limit defined).
Macro-particle limits: EU GMP Annex 1 also sets limits at 5.0 micrometres — Grade A/B at rest allow just 20 per cubic metre, the figure that catches out half the class.
Occupancy states: as-built (installed, no equipment or people), at-rest (equipment running, no people), in-operation (people working) — a classification without its state is meaningless.
Requalification clock: ISO 14644-2 recommends maximum intervals of six months for ISO 5 and better, twelve months for ISO 6 to 8, plus requalification after changes.
Classification is not sterility: the ISO class counts inert particles; viable contamination is monitored separately with settle, contact and active air methods with their own grade limits.
Indian anchor: revised Schedule M (notified end-2023) moves Indian clean-area requirements toward ISO 14644-consistent classification and testing, replacing the older descriptive approach.

Classifying a room in practice

Walk a Grade C room of about 40 square metres before a campaign. The protocol fixes the state (at-rest), and locations come out as the square root of 40 — roughly six positions away from returns and doorways. At each, an optical particle counter samples, and the 0.5 and 5.0 micrometre counts are compared with class limits one location at a time; the 2015 edition abolished the old 95 per cent upper-confidence-limit arithmetic in favour of this per-location pass. A corner near a pass-through hatch reads 380,000 particles at 0.5 micrometre — just over the ISO 7 limit — and the room fails despite a clean average: cleanrooms fail locally, where airflow is disturbed.

What follows separates classification, verification and monitoring: reclassification is this formal protocol-driven survey, while routine monitoring is the daily system of counters and plates at fixed points with alert and action limits set well inside the class — a room can pass classification yet drift operationally. The viable side runs in parallel: settle plates exposed about four hours, contact plates and active air samplers, each with their own grade limits. The filed report records state, locations, counts, calibration and verdict; the next is due within the ISO 14644-2 window, or sooner if the HVAC is modified.

Where students slip

The commonest error is treating ISO class as a sterility grade: class limits count non-viable particles, and a bone-dry ISO 5 room can be microbiologically poor if gowning is careless. The second slip is quoting a class without its occupancy state — EU GMP deliberately allows Grade B to run as ISO 7 in operation because humans shed. Third, the legacy conversions: the retired Federal Standard 209E Class 100 equals ISO 5 and Class 10,000 equals ISO 7, and old question banks still trade on these. Finally, the 5.0 micrometre column is the forgotten one — 20 per cubic metre for Grade A at rest separates prepared candidates from the rest.

Frequently asked questions

What are the particle limits for ISO Class 5 and ISO Class 7?

At 0.5 micrometre and above, ISO 5 allows 3,520 particles per cubic metre and ISO 7 allows 352,000 — successive classes ten-fold apart.

How do EU GMP grades map onto ISO classes?

Grade A is ISO 5 in operation; Grade B is ISO 5 at rest and ISO 7 in operation; Grade C is ISO 7 at rest and ISO 8 in operation; Grade D is ISO 8 at rest.

What do as-built, at-rest and in-operation mean in classification?

Occupancy states: as-built (no equipment or people), at-rest (equipment running, no people) and in-operation (staff working) — every class claim must name its state.

How often must a cleanroom be reclassified?

Per ISO 14644-2, at least every six months for ISO 5 and cleaner rooms and annually for ISO 6 to 8, plus requalification after modifications or failed monitoring.

Does ISO classification guarantee sterility?

No; it counts non-viable particles only, so viable monitoring and the sterilisation or aseptic processes themselves carry the sterility burden.