Buyer guide
ISO 5 and ISO 6 cleanroom requirements
ISO 14644-1:2015 allows up to 3,520 particles of 0.5 µm or larger per cubic metre in an ISO 5 room, and up to 35,200 in an ISO 6 room. The standard sets limits only, so airflow and layout come from your process and your qualification plan, not from the class.
By ZY Cleanroom · Updated · Sources at the end of the page
Particle limits for ISO 5 and ISO 6
ISO 14644-1 counts particles in one cubic metre of air. The limits are cumulative, so a count at 0.5 µm includes every particle at or above that size.
The 2015 edition has no ISO 5 limit at 5 µm. Pharmaceutical users still count 5 µm particles, because EU GMP Annex 1 sets a 29 per cubic metre monitoring limit for Grade A.
| Particle size | ISO 5, per m³ | ISO 6, per m³ |
|---|---|---|
| 0.1 µm and larger | 100,000 | 1,000,000 |
| 0.2 µm and larger | 23,700 | 237,000 |
| 0.3 µm and larger | 10,200 | 102,000 |
| 0.5 µm and larger | 3,520 | 35,200 |
| 1 µm and larger | 832 | 8,320 |
| 5 µm and larger | No table entry | 293 |
State the occupancy state
A class needs a state: as-built, at rest or operational. People and equipment add particles, so the operational target is harder to hold.
Annex 1 shows the effect. A Grade B room has the ISO 5 limit of 3,520 at rest, but 352,000 in operation, which is the ISO 7 limit.
Annex 1 also gives a clean-up guidance value of under 20 minutes to return to the at-rest limits after work stops (para 4.29). Write your own recovery target into the room list.
Airflow reference points
No air change rate comes with the class. These published values are starting points for a design review.
| Source | Value | Applies to |
|---|---|---|
| FDA aseptic guidance, 2004 | 0.45 m/s (90 ft/min), ±20% | Critical area, generally established |
| EU GMP Annex 1, 2022, para 4.30 | 0.36 to 0.54 m/s, guidance value | Unidirectional flow at the working position |
| LBNL survey, 2004 | 0.10 to 0.41 m/s; 100 to 480 air changes per hour | Measured in ISO 5 rooms |
| IEST RP-CC012.1, as cited by LBNL | Lower limit 240 air changes per hour | ISO 5 recommendation |
Example calculation: velocity to air changes
Air changes per hour equal velocity times 3,600 divided by ceiling height. Example only, with an assumed 0.45 m/s and an assumed 3 m ceiling: 0.45 × 3,600 ÷ 3 = 540.
More air costs more fan power. LBNL reports that 10% to 30% more airflow raises fan power by about 30% to 120%.
Where ISO 6 is used
FDA recommends that the area next to an aseptic processing line meets at least ISO 7 in dynamic conditions. A maker may class it ISO 6, or hold the whole filling room at ISO 5.
Put these in the room list
Write the class, the occupancy state, the particle sizes to count, the airflow type and the velocity test position. Add the pressure plan and the recovery target.
Annex 1 qualification tests include filter integrity, airflow, pressure difference, airflow direction, temperature, humidity and recovery. It sets requalification at a maximum of 6 months for Grade A and B, and 12 months for Grade C and D.
Where to count
FDA says air near exposed sterile containers should meet the ISO 5 count when measured at representative locations. These are normally within 1 foot of the work site, in the airflow, during filling and closing.
Counts taken in a quiet corner prove little. Name the count positions in the test plan, and put them where the process is exposed.
Who approves the room
Your regulator or customer auditor judges the facility. The contractor builds to your room list and supplies test data. The owner keeps the responsibility. To have a room list reviewed, send it to ZY Cleanroom, a cleanroom design-and-build contractor with its own panel factory in Tianjin, China.
Questions
Common questions
How many particles are allowed in an ISO 5 room?
ISO 14644-1:2015 allows 3,520 particles of 0.5 µm and larger per cubic metre. The limit at 1 µm is 832.
Is ISO 5 the same as Grade A?
At 0.5 µm the limit is the same, 3,520. Annex 1 adds microbial limits, an airflow guidance value and monitoring rules.
How many air changes does ISO 5 need?
ISO 14644-1 sets none. LBNL measured 100 to 480 per hour in ISO 5 rooms. Size the air from your process and test it.
How far apart are ISO 5 and ISO 6?
Ten times at 0.5 µm: 3,520 against 35,200 particles per cubic metre.
What do Class 100 and Class 1000 cleanroom mean?
They are names from the old US standard FED-STD-209E, cancelled in 2001. The number was the limit of particles of 0.5 µm or larger per cubic foot. Class 100 is treated as the nearest match to ISO 5, and Class 1000 to ISO 6. Use the ISO class in new specifications.
What are the gowning requirements for an ISO 5 cleanroom?
ISO 14644-1 sets no gowning rule, so it depends on the process. For aseptic work, Annex 1 (para 7.13) lists a sterilised suit, sterile headgear, facemask and eye coverings, sterilised gloves and sterilised footwear for Grade B, including access to Grade A. Electronics rooms set their own rules, so write yours into a procedure.
Related guides
- Cleanroom monitoring systems: particles, pressure, temperature and humidity
- Cleanroom failed particle count: causes and fixes
- Cleanroom temperature and humidity requirements
- EU GMP grades A to D compared with ISO classes
- Turnkey cleanroom contractor
- Room list builder
Sources
- ISO 14644-1:2015, Cleanrooms and associated controlled environments, Part 1: Classification of air cleanliness by particle concentration (ISO catalogue entry; published December 2015)
- ISO 14644-1:2015 preview on iTeh Standards, Table 1 (preview copy, cross-checked against the other sources listed; checked 31 October 2026)
- DIN Media, DIN EN ISO 14644-1 (status: current; checked 31 October 2026)
- Cleanroom Technology, Tips for particle concentration compliance under ISO 14644-1:2015 (19 September 2018; checked 31 October 2026)
- FDA, Guidance for Industry: Sterile Drug Products Produced by Aseptic Processing, Current Good Manufacturing Practice (September 2004, nonbinding; checked 31 October 2026)
- EudraLex Volume 4, Annex 1: Manufacture of Sterile Medicinal Products (published 25 August 2022, applied from 25 August 2023; checked 31 October 2026)
- Tengfang Xu, Lawrence Berkeley National Laboratory, Considerations for efficient airflow design in cleanrooms (peer reviewed, 29 July 2004; checked 31 October 2026)
Project enquiry
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WhatsApp +44 7962 561184 is our UK number for export enquiries. The factory is in Tianjin, China.
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