The micron rating of the filters in your water filtration system will determine how effective it is.

The contaminants that are removed will depend on the size of the filter, which can range from 0.0001 to 800 microns.

The higher the micron rating, the bigger the particles it can trap.

Follow us here to learn all you need to know.

What is Micron Filter Rating?

The size of the perforations in the mesh determines the micron filter rating.

This can range from 0.0001 to 800 microns, comprising materials (1)such as nylon, polyester, and polypropylene.

micron rating

To put this is perspective, here are a few examples of particle or micron filter size of day-to-day materials:

Carbon dioxide0.00065 microns
Bacteria0.3 – 60 microns
Tobacco smoke.01 – 4 microns
Fine silt  4 – 8 microns
Human hair40-300 microns

The molecule size of any material will determine whether or not it can pass through a micron filter. If the molecules are bigger than the holes in the mesh, they will be unable to percolate through and will remain in the water or air.

The human eye can see objects that are greater than 40 microns, such as dust mites.

What is the Difference Between Micron and Mesh Filters?

Micron filters comprise various porous materials which have a specific gap size between the fibers.

Mesh filters comprise wire mesh which is measured by a number of strands or threads per linear inch.

You cannot correlate directly between mesh size and microns as the diameter of the wire itself will differ according to its manufacture.

The size of the aperture cannot be used as a micron measurement, as the greater, the number of wire strands present, the smaller the gaps between them will be, reducing the micron size.

Understanding Micron Ratings

One micron measures 1/25400 of an inch, or one inch contains 25,400 microns.

Thus, the greater the micron rating, the greater the size of the particles that can be filtered.

Here is a comparison of different micron sizes:

ParticleParticle Size
Anthrax1 – 5
Antiperspirant6 – 10
Asbestos0.7 – 90
Atmospheric Dust0.001 – 40
Auto and Car Emission1 – 150
Bacteria0.3 – 60
Beach Sand100 – 10000
Bone Dust3 – 300
Bromine0.1 – 0.7
Burning Wood0.2 – 3
Calcium Zinc Dust0.7 – 20
Carbon Black Dust0.2 – 10
Carbon Dioxide0.00065
Cayenne Pepper15 – 1000
Cement Dust3 – 100
Clay, coarse2 – 4
Clay, medium1 – 2
Clay, fine0.5 – 1
Coal Dust1 – 100
Coal Flue Gas0.08 – 0.2
Coffee5 – 400
Combustion0.01 – 0.1
Combustion-related – motor vehicles, wood burning,
open burning, industrial processes
up to 2.5
Copier Toner0.5 – 15
Corn Starch0.1 – 10
Dot (.)615
Dust Mites100 – 300
Eye of a Needle1230
Face Powder0.1 – 30
Fertilizer10 – 1000
Fiberglass Insulation1 – 1000
Fly Ash1 – 1000
Gelatin5 – 90
Ginger25 – 40
Glass Wool1000
Grain Dusts5 – 1000
Gravel, very fine (0.08 inch)2000
Gravel, fine (0.16 inch)4000
Gravel, medium (0.3 inch)8000
Gravel, coarse (0.6 – 1.3 inches)15000 – 30000
Gravel, very coarse (1.3 – 2.5 inches)30000 – 65000
Ground Limestone10 – 1000
Hair5 – 200
Household dust0.05 – 100
Human Hair40 – 300
Human Sneeze10 – 100
Humidifier0.9 – 3
Insecticide Dusts0.5 – 10
Iron Dust4 – 20
Lead, solder radiator manufacturing – mean value1.3
Lead, battery and lead powder manufacturing12 – 22
Lead Dust0.1 – 0.7
Liquid Droplets0.5 – 5
Metallurgical Dust0.1 – 1000
Metallurgical Fumes0.1 – 1000
Milled Flour, Milled Corn1 – 100
Mist70 – 350
Mold3 – 12
Mold Spores10 – 30
Mustard6 – 10
Oil Smoke0.03 – 1
One inch25400
Paint Pigments0.1 – 5
Pesticides & Herbicides0.001
Pet Dander0.5 – 100
Pollen10 – 1000
Radioactive Fallout0.1 – 10
Red Blood Cells5 – 10
Rosin Smoke0.01 – 1
Sand, very fine (0.0025 inch)62
Sand, fine (0.005 inch)125
Sand, medium (0.01 inch)250
Sand, coarse (0.02 inch)500
Sand, very coarse (0.02 inch)500
Saw Dust30 – 600
Sea Salt0.035 – 0.5
Silt, coarse (0.0015)37
Silt, medium (0.0006 – 0.0012 inche)16 – 30
Silt, fine 8 – 13
Silt, very fine4 – 8
Skin flakes0.5 – 10
Smoke from Natural Materials0.01 – 0.1
Smoke from Synthetic Materials1 – 50
Smoldering or Flaming Cooking Oil0.03 – 0.9
Spanish Moss Pollen150 – 750
Spider web2 – 3
Spores from plants3 – 100
Starches3 – 100
Sugars0.0008 – 0.005
Talcum Dust0.5 – 50
Tea Dust8 – 300
Textile Dust6 – 20
Textile Fibers10 – 1000
Tobacco Smoke0.01 – 4
Typical Atmospheric Dust0.001 to 30
Viruses0.005 – 0.3
Yeast Cells1 – 50
Micron Filter Size Chart

5 micron

This will filter out some bacteria, including anthrax, some molds, coffee granules, and paint pigments.

10 micron

This will filter out red blood cells, carbon dust, fertilizers, and insecticides.

Recommended Reading: Best Whole House Water Filters – Reviews + [Guide 2021]

25 micron

This will filter out white blood cells, salt, sand and rust particles.

30 micron

This will filter out algae, solvents, silt and milled flour.

50 micron

This will filter out coal dust, pet dander, human hair, and plant spores.

Which Micron Filter Size is Best for Me?

Before you decide on which filter and which micron is best suited to your needs, you need to know what contaminants or other materials are in your water.

We know that smaller micron sizes will remove more material, but that may slow down your water flow.

Filters with smaller micron ratings will have to be replaced regularly due to the debris they accumulate.

You may find that it is better to have more than one filter that will progressively remove particles in your water. These would be installed from the coarsest to the finest.

Why Does Micron Size Matter?

The smaller the micron size, the more contaminants are removed during the filtration process.

different micron size

If you are mainly concerned with removing bacteria, viruses and parasites, a one micron filter will suffice.

If you need to remove sand and silt and other solids, you will need a larger micron size filter, or a series of filters of different micron sizes.

Smaller micron filters may cost more, but will be better for your health in the long term.

What Are Nominal and Absolute Micron Filters?

All filters, regardless of their micron rating, are effective at removing impurities to some degree.

Nominal filters will remove most of the defined pollutants for its particular rating, from about 60% to 98% efficiency levels.

This will vary according to the extent of the pollution and the environment. The capacity of filters may also vary by manufacturer.

Nominal filters will possibly only remove 70% – 80% of the bacteria that cause Cryptosporidium (2), a form of gastroenteritis that will lead to diarrhea and vomiting.

Absolute filters will filter 100% of contaminants at their micron rating. They are tested more exhaustively, including for:

  • Concentration
  • Identification
  • Particle size
  • Pressure

Absolute filters may be constructed of a solid layer like ceramic, metal or Teflon. The holes are a regular size and are created using a nuclear (3)process.

Absolute filters are used in extreme sterile environments such as NASA.

To ensure that a filter is ‘absolute’, it should include the wording “NSF 53” or “NSF 58” as well as “cyst reduction” or “cyst removal”. Any product that does not feature one or more of these clauses cannot be deemed to be an absolute filter.

What Micron Filter Do I Need for My Well Water?

Filters with micron sizes of between 0.5 – 2 will remove the majority of water contaminants.

You may want to install depth filters, where the micron sizes vary from larger to smaller. The larger holes trap larger toxins and scale down to smaller micron ratings that will catch bacteria and viruses.

Our Recommended Sediment Filter for Well Water in 2021

For water sources with a large surface area, you may consider a pleated filter that can net substances between 30-500 microns. These can also be used for finer filtration of required.


Whatever filtration system you are using, it will be necessary to consider the micron rating of each filter.

The micron ratings used in various categories of filtration include:

Reverse osmosis0.0001 micron
Nanofiltration .001 micron
Ultrafiltration.01 micron
Microfiltration0.1 micron
Particle filtration0.3 micron

All filters must be inspected and either cleaned or replaced at least once a year, or more often if you deem it necessary.

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