The micrometre as used by the International Bureau of Weights and Measures; symbol: µm with an American spelling of SI of length equaling 1×10−6 of a metre (SI standard prefix "micro-" = 10−6); that is, one-millionth of a metre (or one-thousandth of a millimetre, 0.001 mm, or about 0.000039 inch)
- Particle size=17–20 Controlled contaminant=0.3 μm Typical Application=Virus, carbon dust, sea salt, smoke Electronics & pharmaceutical manufacturing cleanroom
- 13–16 0.3–1.0 μm Bacteria, droplet nuclei (sneeze), cooking oil, most smoke and insecticide dust, most face powder, most paint pigments hospital & general surgery
- 9–12 1.0–3.0 μm Legionella, Humidifier dust, Lead dust, Milled flour, Auto emission particulates, Nebulizer droplets Superior residential, better commercial, hospital laboratories
- 5–8 3.0–10.0 μm Mold, spores, dust mite debris, cat and dog dander, hair spray, fabric protector, dusting aids, pudding mix Better residential, general commercial, industrial work spaces
- 1–4 > 10.0 μm Pollen, dust mites, cockroach debris, sanding dust, spray paint dust, textile fibers, carpet fibers Residential window AC unit
