How to Choose an In-line Filter – Mesh and Particle Size

Color surface-filtration graphical representationFilter Mesh, Microns and In-line Filter Choice
Filtration is filtration right? Well, like all things technical it is not as simple as that when it comes to particle separation. The easiest way to start thinking about in-line filter choice is by looking first at filter mesh. In this post I want to give you a simple mental picture of what filter mesh or screen is and an overview of how different sizes of mesh are described.

Filtration Basics
Fishing net is basically a filter used to separate fish from water. Like fishing net, filter mesh is woven metal wire or plastic strands which stops particles that are too large from passing through openings in the mesh. Filter mesh is considered a surface filtration type of material or media because particles are captured on the surface of the mesh.

What a surface filter can do:

  • Capture particles that cannot pass through holes in the mesh
  • Be easily cleaned using backwashing


An exploded view of an ISM modular check valve. Click here to go to a landing page where you can get more information about these valves.

Modular Check Valves

We've taken spring-loaded check valves to a whole new level. Mix and match imperial and metric connections. Watch the video.

A play button for a video about ISM's modular check valves. Click here to go to a landing page where you can watch the video.

Why Size Matters
Just as a fish net used to catch salmon cannot catch minnows, you need to choose a useful filter mesh. When choosing a mesh, you need to remember that mesh numbers and mesh sizes are not the same thing.


Mesh Number
You will often see the US Standard Mesh number used to describe mesh size. The US Standard Mesh number is the number of openings per inch of mesh. The larger the mesh numbers the greater the number of openings per inch and the smaller the openings in the mesh. Convert US Standard Mesh to microns, inches and millimeters.

Mesh Size
Mesh size is the actual size of the openings in the mesh. This is usually given in fractional inches and millimeters and/or microns. A micron (μm) is one thousandth of a millimeter or one twenty-five thousandth of an inch.

Strand Diameter
Descriptions of mesh include the diameter of the strands used in the weave. Mesh made with the same mesh number but made with thicker strands will have smaller mesh openings.

For more help understanding the relationship between mesh number, mesh size and microns check out our Mesh and Micron Sizes resource as well as this online mesh calculator.

How Much is Too Much?
The higher the mesh number the more surface area is taken up just by the strands. The surface area of the mesh openings as a percentage of the total surface area of the mesh is the Percent Open Area (POA). A higher POA means a greater flow.

Well, there you have it; a brief outline of some of the technical issues that come up when describing filter mesh. You need to keep these points in mind when thinking about filter mesh as it relates to the selection of the proper in-line filter for your application:

  • Mesh is a type of surface filtration that can be cleaned by backwashing.
  • Mesh is made in a variety of metals, metal alloys and plastics.
  • Mesh number is not mesh size. It is the number of openings per inch.
  • Mesh size (pore size) is usually given in fractional inches and millimeters and/or microns.
  • Filament diameter affects both the mesh opening size and the percent open area.
  • The higher the percent open area of a mesh, the higher the flow the mesh can handle.


Look for our upcoming blog article for a discussion of chemical compatibility:

How to Choose an In-line Filter – Chemical Compatibility

Have you had a hard time trying to match particle size with in-line filter specs? Help us by telling others about it and what you learned.

Still have questions about how to select the right in-line filter for your application? If so, send me an email – You can also ask questions using the comments section below.


Steven C. Williams headshot March, 2018.

About the author
Steven C. Williams, BS, is the technical writer and an inbound marketing specialist at Industrial Specialties Manufacturing (ISM), an ISO 9001-2015 supplier of miniature pneumatic, vacuum and fluid circuitry components to OEM's and distributors all over the world. He writes on technical topics related to miniature pneumatic and fluidic components as well as topics of general interest at ISM.       
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