Filter Bag Micron Ratings Explained

One micron is a unit of length equal to one millionth of a meter, using the symbol: μm.

Filter micron levels specify the average size opening in the filter media. If a polyester fiber filter bag is rated for 20-micron filtration, the average size opening between fibers is 20 micron.

Typically, filter media is given a micron rating based on an 80% efficiency, meaning that the filter will remove 80% of contaminants greater than 20-micron if you are using a filter bag rated for 20 micron.

Nominal vs Absolute Micron Ratings

Most filter bags are rated with what’s called a “nominal” micron rating, meaning that a percentage of particles larger than the specified micron rating will pass through the bag. An “absolute” micron rating will filter 99.9% of particles at the specified micron rating.

Absolute-rated bag filters are significantly more expensive when compared to a nominal-rated bag filter. For most applications, using a nominal-rated filter bag allows for users to achieve the desired end result or product at a much more affordable cost.

Approximate Micron of Common Materials

	Particle Size in Microns
Coffee	4 - 400 *
Corn Starch	0.1 - 0.8 *
Clay (coarse)	2 - 4 *
Clay (medium)	1 - 2 *
Clay (fine)	0.5 - 1 *
Dust Mites	100 - 300 ****
Fertilizer	10 - 1000 *
Gelatin	5 - 90 *
Gravel (very fine)	2000 *
Gravel (fine)	4000 *
Gravel (medium)	8000 *
Gravel (coarse)	15000 - 30000 *
Gravel (very coarse)	30000 - 65000 *
Ground Limestone	10 - 1000 *
Human Hair (diameter)	70 ***
Lead (solder radiator manufacturing)	1.3 *
Lead (battery and lead powder manufacturing)	12 - 22 *
Lead Dust	0.1 - 0.7 *
Mold	3 - 12 *
Mold Spores	10 - 30 *
Naked-Eye Visibility	40 ***
Pollen	10 - 1000 *
Red Blood Cell	12 **
Sand (fine)	250 **
Sand (beach)	700 **
Sea Salt	0.035 - 0.5 *
Silt (coarse)	37 *
Silt (medium)	16 - 30 *
Silt (fine)	8 - 13 *
Silt (very fine)	4 - 8 *
Spores from Plants	3 - 100 *
Starches	3 - 100 *
Sugars	0.0008 - 0.005 *
Tea Dust	8 - 300 *
White Blood Cell	25 ***