Under European normalization standards EN 779, the following filter classes were recognized:
| Usage | Class | Performance | Performance test | Particulate size approaching 100% retention |
Test Standard |
|---|---|---|---|---|---|
| Coarse filters
(used as Primary) |
G1 | 65% | Average value | >5 μm | BS EN779 |
| G2 | 65–80% | Average value | >5 μm | BS EN779 | |
| G3 | 80–90% | Average value | >5 μm | BS EN779 | |
| G4 | 90%– | Average value | >5 μm | BS EN779 | |
| Fine filters
(used as Secondary) |
M5 | 40–60% | Average value | >5 μm | BS EN779 |
| M6 | 60–80% | Average value | >2 μm | BS EN779 | |
| F7 | 80–90% | Average value | >2 μm | BS EN779 | |
| F8 | 90–95% | Average value | >1 μm | BS EN779 | |
| F9 | 95%– | Average value | >1 μm | BS EN779 | |
| Semi HEPA | E10 | 85% | Minimum value | >1 μm | BS EN1822 |
| E11 | 95% | Minimum value | >0.5 μm | BS EN1822 | |
| E12 | 99.5% | Minimum value | >0.5 μm | BS EN1822 | |
| HEPA | H13 | 99.95% | Minimum value | >0.3 μm | BS EN1822 |
| H14 | 99.995% | Minimum value | >0.3 μm | BS EN1822 | |
| ULPA | U15 | 99.9995% | Minimum value | >0.3 μm | BS EN1822 |
| U16 | 99.99995% | Minimum value | >0.3 μm | BS EN1822 | |
| U17 | 99.999995% | Minimum value | >0.3 μm | BS EN1822 |
Source: Air filters, Wikipedia