Mesh size is the number of openings in one linear inch of a screen or sieve. A 10-mesh screen has 10 openings per inch, a 100-mesh screen has 100 openings per inch, and so on. The higher the mesh number, the smaller each individual opening, which means finer filtration or sorting. This single concept underlies particle sizing across industries from construction to pharmaceuticals to irrigation.
How Mesh Numbers Work
The measurement is straightforward: stretch a ruler across one inch of woven wire screen and count the openings. That count is the mesh number, sometimes called mesh count or lines per inch (LPI). A #10 mesh screen has 10 openings (and 10 wires) per linear inch in each direction, so you might see it written as “10 × 10 mesh.” A #400 mesh screen packs 400 openings into that same inch, creating extremely tiny holes.
The key relationship to remember is that mesh number and opening size move in opposite directions. Low mesh numbers mean large openings and coarse filtering. High mesh numbers mean tiny openings and fine filtering. A 10-mesh screen has openings of about 2,000 microns (2 mm), while a 400-mesh screen has openings of just 37 microns, roughly half the width of a human hair.
Mesh to Micron Conversion
Because mesh number alone doesn’t tell you the exact size of the opening in standard units, most industries rely on conversion charts. Here are the most commonly referenced mesh sizes and their approximate opening dimensions:
- 10 mesh: 2,000 microns (2.0 mm)
- 20 mesh: 850 microns (0.85 mm)
- 40 mesh: 420 microns (0.42 mm)
- 60 mesh: 250 microns (0.25 mm)
- 100 mesh: 149 microns (0.149 mm)
- 200 mesh: 74 microns (0.074 mm)
- 325 mesh: 45 microns
- 400 mesh: 37 microns
These values come from the U.S. standard (ASTM) sieve series. You’ll notice the relationship isn’t perfectly linear. Doubling the mesh number doesn’t exactly halve the opening size, because wire thickness takes up space too. That’s an important detail covered below.
Why Wire Diameter Matters
Two screens can have the same mesh count but different opening sizes if they’re woven from different thickness wire. Thicker wire takes up more of each linear inch, leaving smaller gaps between the strands. Thinner wire leaves more open space. This is why conversion charts specify both mesh number and wire diameter to give a precise opening measurement.
The practical impact shows up as “open area,” the percentage of the screen that is actual open space rather than wire. A screen with thin wire and high open area lets more material flow through per unit of time, while a screen with thicker wire is stronger but restricts flow. In filtration systems, this tradeoff between flow rate and structural strength matters a lot. In lab sieves, the wire diameter is tightly controlled by standards so that a given mesh number always produces a predictable opening size.
ASTM and Tyler Standards
The two most widely used systems for standardizing mesh sizes are the ASTM E11 standard and the Tyler Standard Screen Scale. In practice, they align closely. A Tyler 40 mesh corresponds to an ASTM No. 40 sieve, a Tyler 200 mesh matches ASTM No. 200, and so on through most of the range. The ASTM standard, currently designated E11-24, covers sieve cloth with openings from 125 mm down to 20 microns. It specifies three tolerances for each sieve: the average opening size, the maximum allowable opening, and the maximum standard deviation across openings. These tolerances ensure that when you buy a No. 200 sieve, its openings are reliably around 74 microns regardless of the manufacturer.
ASTM designations are also available as ISO equivalents, which makes the system internationally compatible. If you’re working with European or Asian suppliers, you can cross-reference mesh numbers to their metric equivalents without ambiguity.
Common Uses by Mesh Range
Different mesh ranges serve different purposes, and knowing the general categories helps you pick the right screen for your application.
Coarse meshes (4 to 20 mesh, openings from about 5 mm down to 850 microns) handle gravel screening, large aggregate sorting, and basic debris removal. In geology, the Wentworth scale classifies gravel as anything above 2 mm, so a 10-mesh sieve (2,000-micron openings) sits right at the boundary between gravel and sand. Construction projects use sieves in this range to grade aggregate for concrete and asphalt.
Medium meshes (20 to 100 mesh, roughly 850 down to 149 microns) cover most sand classification. Sand is defined as particles between 2 mm and 62.5 microns, so this range captures the bulk of sand grading work. It’s also where you find screens for grain processing, fertilizer sizing, and general industrial screening.
Fine meshes (100 to 400 mesh, 149 down to 37 microns) enter the territory of silt-sized particles and fine powders. Pharmaceutical companies, paint manufacturers, and chemical processors work in this range. Lab analysis of soil composition typically uses sieves at 200 mesh and above to separate silt from sand. Below about 325 mesh (45 microns), you’re filtering particles invisible to the naked eye.
Mesh Size in Filtration Systems
If you’re shopping for water filters, irrigation screens, or industrial strainers, you’ll encounter mesh size as the primary specification. The inverse relationship between mesh count and micron rating is critical here: higher mesh means smaller micron rating means finer filtration.
For irrigation, an 80-mesh screen (approximately 177 microns) works well for micro sprinklers, which can tolerate moderate particle sizes. Drip irrigation systems with medium to high flow rates typically need 120-mesh screens (about 130 microns), while low-flow drip emitters require 150-mesh (around 100 microns) to prevent clogging. Choosing too coarse a filter risks blocked emitters; choosing too fine a filter restricts water flow and requires more frequent cleaning.
In household water filtration, you’ll sometimes see micron ratings used instead of mesh numbers, especially for filters finer than 400 mesh. At that point, manufacturers switch to micron ratings (typically 25, 10, 5, or 1 micron) because the mesh numbering system becomes less intuitive at extreme fineness.
How to Read a Mesh Size Specification
When you see a product labeled with a mesh range like “40/60 mesh,” it means the particles passed through a 40-mesh screen (openings of 420 microns) but were caught by a 60-mesh screen (openings of 250 microns). So the particles are between 250 and 420 microns in diameter. This notation is standard for specifying particle size distributions in products like sandblasting media, filter sand, and powdered chemicals.
A single mesh number on a filter or screen simply tells you the finest particle it will block. A 100-mesh strainer catches anything larger than about 149 microns. Anything smaller passes through. If you need to capture finer particles, you need a higher mesh number, which means smaller openings and, in most cases, slower flow rates. That basic tradeoff between precision and throughput applies to virtually every screening and filtration application.