Particle Sizes

Sizes of airborne particle as dust,
pollen bacteria, virus and many more

The size of contaminants and particles are usually described in microns,
a metric unit of measure where one micron is one-millionth of a meter.

micrometer (µm): a common metric unit of distance equal to 0.001 millimeter; or about 0.039 370 mil. The name micron is also used for this unit.

microgram (µg or mcg)
1/1,000,000 of a gram (1 × 10^-6), or 1/1000 of a milligram
is one of the smallest units of weight/mass commonly used.

There are 25,400 microns in one inch.
The eye can see particles to about 40 microns.
(some reports say as low as 10 microns)
Online Metric Conversion Calculators

The size of some contaminants and particles are indicated in the table below.

Particle	Particle Size (microns)
one inch	25,400
dot (.)	615
Eye of a Needle	1,230
Glass Wool	1000
Spanish Moss Pollen	150 - 750
Beach Sand	100 - 10000
Mist	70 - 350
Fertilizer	10 - 1000
Pollens	10 - 1000
Cayenne Pepper	15 - 1000
Textile Fibers	10 - 1000
Fiberglass Insulation	1 - 1000
Grain Dusts	5 - 1000
Human Hair	40 - 300
Human Hair	60 - 600
Dust Mites	100 - 300
Saw Dust	30 - 600
Ground Limestone	10 - 1000
Tea Dust	8 - 300
Coffee	5 - 400
Bone Dust	3 - 300
Hair	5 - 200
Cement Dust	3 - 100
Ginger	25 - 40
Mold Spores	10 - 30
Starches	3 - 100
Red Blood Cells	5 - 10
Mold	3 - 12
Mustard	6 - 10
Antiperspirant	6 - 10
Textile Dust	6 - 20
Gelatin	5 - 90
Spider web	2 - 3
Spores	3 - 40
Combustion-related Carbon Monoxide from motor vehicles, wood burning, open burning, industrial processes	up to 2.5
Fly Ash	1 - 1000
Milled Flour, Milled Corn	1 - 100
Coal Dust	1 - 100
Iron Dust	4 - 20
Smoke from Synthetic Materials	1 - 50
Lead Dust	2
Face Powder	0.1 - 30
Talcum Dust	0.5 - 50
Asbestos	0.7 - 90
Calcium Zink Dust	0.7 - 20
ClickPaint Pigments	0.1 - 5
Auto and Car Emission	1 - 150
Metallurgical Dust	0.1 - 1000
Metallurgical Fumes	0.1 - 1000
Clay	0.1 - 50
Humidifier	0.9 - 3
Copier Toner	0.5 - 15
Liquid Droplets	0.5 - 5
Insecticide Dusts	0.5 - 10
Anthrax	1 - 5
Yeast Cells	1 - 50
Carbon Black Dust	0.2 - 10
Atmospheric Dust	0.001 - 40
Smoldering or Flaming Cooking Oil	0.03 - 0.9
Corn Starch	0.1 - 0.8
Sea Salt	0.035 - 0.5
Bacteria	0.3 - 60
Bromine	0.1 - 0.7
Lead	0.1 - 0.7
Radioactive Fallout	0.1 - 10
Rosin Smoke	0.01 - 1
Combustion	0.01 - 0.1
Smoke from Natural Materials	0.01 - 0.1
Burning Wood	0.2 - 3
Coal Flue Gas	0.08 - 0.2
Oil Smoke	0.03 - 1
Tobacco Smoke	0.01 - 4
Viruses	0.005 - 0.3
Typical Atmospheric Dust	0.001 to 30
Sugars	0.0008 - 0.005
Pesticides & Herbicides	0.001
Carbon Dioxide	0.00065
Oxygen	0.0005

Airborne particles

Airborne particles are solids suspended in the air.

Larger particles - larger then 100 μm

terminal velocities > 0.5 m/s
fall out quickly
includes hail, snow, insect debris, room dust,
soot aggregates, coarse sand, gravel, and sea spray

Medium-size particles - in the range 1 to 100 μm

sedimentation velocities greater than 0.2 m/s
settles out slowly
includes fine ice crystals, pollen, hair, large bacteria,
windblown dust, fly ash, coal dust, silt, fine sand, and small dust

Small particles - less than 1 μm (submicron)

falls slowly, take days to years to settle out of a quiet atmosphere.
In a turbulent atmosphere they may never settle out
can be washed out by water or rain
includes viruses, small bacteria, metallurgical fumes,
soot, oil smoke, tobacco smoke, clay, and fumes

Hazardous Dust Particles

Smaller dust particles can be hazardous for humans. In many jurisdictions dust fractions at specified particle sizes in working environments are required to be measured.

Inhalable Dust

Airborne particles which can enter the nose and mouth during normal breathing. Particles of 100 microns diameter or less.

Thoracic Dust

Particles that will pass through the nose and throat, reaching the lungs. Particles of 10 microns diameter and less. Referred to as PM₁₀ in the USA.

Respirable Dust

Particles that will penetrate into the gas exchange region of the lungs. A hazardous particulate size less than 5 microns. Particle sizes of 2.5 micron (PM_2.5) are often used in USA