Reviewed by: Rob Burnley, Aftersales Manager, Farleygreene.
Summary
Mesh selection starts with the largest particle that must be allowed to pass, not with the particle you want to remove. Specify an aperture slightly larger than that particle, then check that the open area of the mesh supports the throughput required and that the mesh type and wire diameter suit the material and application.
Aperture, wire diameter and mesh material together make a complete specification; a mesh count alone does not, because two meshes with the same count can have different apertures. Below roughly 100 microns, consider ultrasonic deblinding as part of the specification. Validate the final choice on your own product.
On this page:
- How do I select the right mesh aperture for my product?
- What is the difference between aperture and mesh count?
- How does open area affect throughput?
- Should I specify woven, perforated or wedgewire mesh?
- How many mesh decks do I need, and when is grading required?
- Why does the same mesh size behave differently on two different powders?
- What causes mesh blinding and how is it prevented?
- How often should sieve mesh be replaced?
- Quick reference table: what to record before specifying mesh
- Typical mesh sizes, mesh counts and open areas
- How to start a mesh enquiry
How do I select the right mesh aperture for my product?
Answer: Specify an aperture slightly larger than the largest particle that must be allowed to pass, not the size of the particle you are trying to remove. For check sieving that single decision sets the mesh. For grading it sets the finest mesh, and the other decks are worked back from the cuts required.
Why: A sieve separates by allowing true fines (meaning product smaller than the aperture) to pass while rejecting true oversize (meaning product larger than the aperture). Working from the contaminant you want to catch rather than the product you need to keep is a common specification mistake, particularly when a process is being reviewed or a mesh is being reordered from incomplete records. It can produce an aperture that is too coarse, allowing unacceptable oversize to pass, or too fine, reducing yield by rejecting acceptable product.
Once the aperture is set, two further checks are needed: the open area must support the throughput required, and the wire diameter and mesh type must be suitable for the material and application.
How to decide:
- Record the largest particle size that is acceptable in the finished product, with a tolerance, and specify the aperture from that figure.
- State separately what you are removing, whether that is foreign bodies, agglomerates or an oversize fraction, because it changes the outlet arrangement rather than the aperture.
- Check the aperture against the throughput required before committing, because a finer aperture at the same open area reduces the rate the machine can pass.
- Analyse your particle size distribution for “near-size” particles (those within ±15% of your target aperture). A high concentration of near-size particles increases the risk of pegging (particles becoming wedged point-first in screen openings) which requires proactive selection of mechanical or ultrasonic clearing assets.
- Below approximately 100 microns, assess whether ultrasonic deblinding should form part of the specification, based on the powder characteristics required throughput and product performance.
- Validate the aperture on your own material. Product testing is often the quickest way to confirm the optimum specification before committing to production.
When this advice may not apply: Where the product is fibrous, flaky or highly elongated, aperture alone is a poor predictor of what will pass, because such particles present their narrow dimension to the mesh. Pharmaceutical and nutraceutical capsules and tablets are the clearest case, and are usually handled with parallel bars set to a defined width rather than with woven mesh. Vertical bars are also fitted in place of mesh where the aim is to sort bulky material by size, letting the product fall between the bars rather than sifting out the fines. Near-size material, particle shape, the separation efficiency required and a broad particle size distribution can all move the effective cut point away from the nominal aperture, so confirm the choice by testing on your actual product.
What is the difference between aperture and mesh count?
Answer: Aperture is the measurement between the wires of the mesh (in other words, the size of the hole) quoted in millimetres or microns. Mesh count, written as #mesh, measures something different: the number of apertures per linear inch, carrying no units. The two are not interchangeable, because two meshes of the same mesh count can have different apertures.
Why: The difference is wire diameter. Mesh count measures the pitch of the weave, which is the aperture plus the wire diameter, so a mesh woven from thicker wire at the same count has a smaller hole. This is why a specification given only as a mesh count is often incomplete, and why many customers find it helpful to confirm aperture and wire diameter before reordering.
A complete mesh specification therefore has three figures: the aperture in millimetres or microns, the wire diameter in millimetres, and the material. Units are worth stating explicitly: there are 1,000 microns to a millimetre, so a 0.5 mm aperture and a 500 micron aperture are the same screen.
In millimetres, mesh count equals 25.4 divided by the pitch. Farleygreene’s table of typical sizes lists a 0.500 mm aperture woven with 0.160 mm wire at a mesh count of 38: the pitch is 0.660 mm, and 25.4 divided by 0.660 is 38.48, which rounds to the 38 listed.
How to decide:
- Quote aperture and wire diameter together on every enquiry, in millimetres or microns, and treat mesh count as a secondary reference.
- Where an existing specification records only a mesh count, measure the aperture and wire diameter from the screen in service before reordering.
- Use microns consistently below one millimetre and millimetres above it, to avoid the decimal point errors that cause the wrong screen to be ordered.
- Record the mesh material as part of the specification, since the same aperture in a different alloy or in nylon behaves and wears differently.
- Ask which standard the mesh is made to. For industrial woven wire cloth, ISO 9044 defines the terms and sets the permissible errors, requirements and test methods.
When this advice may not apply: This comparison applies to woven wire only. Perforated sheet is specified by hole size and pattern, and wedgewire by slot width, so neither is described by a mesh count.
At Farleygreene we usually ask only for aperture and material grade at this point, together with the component or machine serial number if you are an existing customer. New customers will often send product to us for testing at our test facilities, where we can advise on further specifications.
How does open area affect throughput?
Answer: Open area is the proportion of the screen that is hole rather than wire, expressed as a percentage. It is a major factor in throughput, because product cannot pass where wire sits. Other factors include feed rate, bed depth, product flowability, vibration setting, deblinding, residence time and mesh tension.
Why:
For plain square-weave mesh, open area is calculated by dividing the aperture squared by the square of the sum of the aperture and the wire diameter, then multiplying by 100.
As a formula:
Open Area (%) = A² ÷ (A + d)² × 100
Where:
- A = aperture size
- D = wire diameter
- Both values are expressed in the same unit
The consequence is that at any given aperture, a thinner wire gives a higher open area and a higher throughput, and a shorter mesh life, because thinner wire is weaker and breaks sooner. Finding the right balance between throughput and mesh life is often one of the key decisions in a high-throughput application. It is a commercial decision as much as a technical one, since the gain in rate is paid for in replacement frequency. Perforated sheet sits at the far end of the same trade-off, with a low open area by design, and is chosen where a precise and unchanging aperture matters more than the rate the screen can pass.
Farleygreene’s table of typical sizes shows how much wire diameter matters. A 0.075 mm aperture woven with 0.036 mm wire has an open area of 45.7%, while a 0.150 mm aperture woven with 0.100 mm wire has an open area of 36.0%. Although the first screen has the smaller aperture, it provides a greater proportion of open area because the wire diameter is smaller relative to the aperture size. Across the whole table, open area ranges from 36 per cent at 0.150 mm to 79 per cent at 12.500 mm and 16.000 mm. For combinations beyond a supplier’s table, ISO 4783-1 tabulates a comprehensive range of aperture and wire diameter combinations, with the percentage open area of each stated.
How to decide:
- Farleygreene confirms the open area figure for each specification, so it can be requested alongside the aperture and wire diameter when comparing quotations.
- Where throughput is the limiting factor, a thinner wire at the same aperture may recover some of the rate, which is worth testing before considering a larger machine.
- Where the product is abrasive, a heavier wire with a lower open area may last longer, so expected throughput and replacement interval are best considered together.
- Mesh options compare best on cost per operating hour, which combines screen price, expected life and the throughput each delivers.
- Where a screen is failing early, a previous specification change may have traded wire diameter for throughput, so the earlier specification is worth checking.
When this advice may not apply: Where throughput is limited by blinding rather than by open area, increasing the open area will not help, because the apertures are being closed by the product rather than being too few. Diagnose blinding first.
At Farleygreene, we calculate the optimum open area for customers, providing full support to ensure that all factors are taken into account to give you the best throughput for your needs.
Should I specify woven, perforated or wedgewire mesh?
Answer: Woven wire is the default for most applications and offers the widest range of apertures and the highest open area. Perforated sheet is specified where aperture accuracy and screen durability matter more than throughput. Wedgewire is used mainly on centrifugal sieves, where its slotted profile resists blocking and gives very consistent throughput.
Why:
Woven mesh is made from metal, nylon or other materials woven into a grid, and it covers the great majority of sieving applications. Stainless steel is the most common material. It provides strength and resists heat, so it suits hot material and applications where a large amount of product remains on the screen, and it keeps its size integrity even on larger meshes.
Woven mesh needs careful handling to avoid damage or warping, and it will eventually break, so regular inspection and planned replacement are part of running it, both to protect throughput and to prevent product loss if a wire fails during a run.
Stainless steel grades
- SS304 is the general purpose grade of stainless steel
- SS316 contains molybdenum for better resistance to chlorides and acids.
- SS430 magnetic mesh is a ferritic stainless steel that contains chromium and is essentially nickel-free, making it naturally magnetic and typically more cost-effective than SS304 or SS316. Its magnetic properties can help downstream rare-earth magnets recover wire fragments in the event of mesh failure. However, its corrosion resistance is significantly lower than that of SS304 and SS316, so suitability should be assessed against the product, cleaning regime and operating environment..
- 318LN mesh is a nitrogen-strengthened austenitic-ferritic steel that is highly corrosion resistant, but it is available in only a very limited range of apertures.
Perforated mesh is made from sheets punched to square or round apertures. The sheets are supplied cut to size and can be bonded to rings in the same way as woven mesh. They are available in most types of stainless steel and they are extremely hard wearing and stable in use. The aperture is highly accurate and consistent, but the open area is reduced, so throughput is lower than woven mesh at the same nominal aperture and capacity rates should be confirmed before it is specified. It comes in a limited range of sizes, typically to a whole or half millimetre.
Wedgewire screens are fabricated as flat panels or tubes, with wedge-profile wires and support profiles resistance welded to give accurate slot dimensions. Product passes through the slot without wedging in it, which makes the screen much harder to block and gives very consistent throughput rates. Its open area is lower than woven wire and it is expensive to manufacture, which is why it is normally seen on centrifugal machines and occasionally on linear screeners rather than as a general-purpose option.
How to decide:
- For most applications, woven wire is the best starting point unless the process places particular demands on durability, aperture stability or resistance to blinding.
- Choose perforated sheet where a precise and unchanging aperture is a quality requirement, or where screen failure during a run carries an unacceptable contamination risk, and accept the throughput reduction.
- Where a broken wire would be a contamination risk, consider SS430 magnetic mesh so that fragments can be recovered by magnet, and weigh its lower corrosion resistance against the product and the cleaning regime.
- Expect wedgewire where a centrifugal machine has been selected, and factor its cost into the spares budget rather than the capital cost alone.
- For abrasive materials, ask about hardened or specialist mesh materials and get a realistic replacement interval for budgeting.
- Confirm that the mesh type you specify is compatible with the deblinding method on the machine, particularly where ultrasonics are fitted.
When this advice may not apply: Where a broken wire would be caught immediately downstream by a metal detector or a second check sieve, the durability argument for perforated sheet weakens considerably, and the throughput advantage of woven wire usually wins.
How many mesh decks do I need, and when is grading required?
Answer: Check sieving needs one mesh. Grading needs a deck (one of the individual mesh layers stacked inside the machine) for each cut or separation point. Up to three meshes of decreasing aperture can be stacked in a single machine, giving up to four fractions. More cuts than that require either a second machine or a cascade of single-mesh sieves.
Why: Check sieving, sometimes called police sieving, is by far the most common application and accounts for the large majority of sieves in service. It uses a single mesh to remove foreign bodies, oversize particles and agglomerates, and it functions as a quality control point rather than as a separation step.
Grading is a more precise operation that aims to produce exact cuts, with the particles in each cut falling between defined sizes. Up to three meshes of decreasing aperture can be stacked in one machine, and a second machine can be added to produce further cuts.
Why does the same mesh size behave differently on two different powders?
Answer: Because aperture is only one of the variables. Particle size, density, moisture content, flowability and particle shape all change how a powder behaves on a screen, so a mesh that runs well on one product can blind or lose efficiency on another. Even where products appear similar on paper, it’s good practice to validate the mesh specification on each product individually. Where there is uncertainty, product testing can quickly identify the most suitable aperture and help avoid unnecessary yield losses.
Why: Two powders with the same nominal particle size can present very differently to the same aperture. A dense free-flowing granule passes readily. A light electrostatic powder of the same nominal size clings to the wire and closes the apertures, blinding the screen. Moisture makes a marginal powder cohesive, and irregular particle shape means the dimension presented to the aperture is not the dimension quoted in the particle size distribution. This is why a mesh specification is properly recorded against a product rather than against a machine, and why a plant running several products through one sieve normally holds a different mesh frame for each rather than compromising on one. Where the same mesh must run several products, that becomes a constraint on the aperture chosen and should be stated at the specification stage.
How to decide:
- Record the mesh specification against each product, not against the machine, and keep the record with the changeover procedure.
- Measure moisture and flowability at the point the product reaches the sieve rather than relying on the specification of the incoming ingredient.
- Where one mesh must run several products, validate the specification against the most difficult material to screen and assess the performance and yield implications for the remaining products
- Note particle shape explicitly for flakes, fibres and elongated particles, since these will not behave as their nominal size suggests.
- Re-validate the mesh when a formulation, a supplier or an upstream process step changes, not only when throughput falls.
When this advice may not apply: For a single product line running a consistent formulation from a stable ingredient source, a validated mesh specification will often remain suitable over the long term. In these cases, routine inspection for screen wear, damage and aperture enlargement is usually more important than re-evaluating the mesh specification itself.
What causes mesh blinding and how is it prevented?
Answer: Blinding is a common challenge when screening fine or difficult powders and occurs when particles lodge in the apertures and progressively close the screen. This typically occurs with powders that are fine, light, electrostatic or slightly moist. Ultrasonic deblinding, which applies vibration directly to the mesh, is the most effective prevention. Mechanical deblinding aids, adjusting vibration amplitude, and reviewing the aperture are the lower-cost alternatives to test first.
Why: A blinded screen behaves exactly like an undersized machine: throughput falls, oversize builds on the mesh and efficiency drops, which is why blinding is often misdiagnosed as a capacity problem. The distinction is between particles wedged in the apertures (which is blinding) and material bridging across the surface in lumps (which is agglomeration and needs mechanical action rather than deblinding). Inspecting the mesh immediately after a run tells you which you have. Below roughly 100 microns, many powders benefit from ultrasonic deblinding to maintain throughput, depending on their characteristics. Mesh specification also influences blinding performance: a higher open area can help, but near-size particles and powder characteristics usually matter more.
How to decide:
- Inspect the mesh straight after a run, before changing anything, since what is left on the screen shows whether the problem is blinding or agglomeration.
- Check the feed rate first, since an overloaded screen can show the same symptoms as a blinded one.
- Try amplitude adjustment and a review of the aperture before specifying new equipment.
- For powders below approximately 100 microns, evaluate ultrasonic deblinding early in the specification process rather than treating it solely as a corrective measure after performance issues arise.
- Confirm that any deblinding method is compatible with the mesh type and the hygiene requirements of the product.
When this advice may not apply: Where the material is highly cohesive, sticky, fatty or has consolidated during storage, poor performance may be caused by agglomeration and adhesion rather than blinding alone. Ultrasonic deblinding can still be effective, but heavily agglomerated products may benefit from a centrifugal sieve, which combines screening with deagglomeration.
How often should sieve mesh be replaced?
Answer: There is no single replacement interval that suits every application, as mesh life depends heavily on the product being processed and the operating conditions. Mesh should be inspected regularly for wear, distortion and enlarged apertures, especially when sieving abrasive materials which shorten mesh life considerably. Holding a spare mesh frame is worth considering where production continuity is critical, since a failed screen otherwise stops production.
Why: There are three main ways in which a sieve mesh can fail, each of which has implications for quality control.
- A wire breaks: oversize passes straight into finished product, and the broken wire itself becomes a foreign body risk.
- The mesh aperture enlarges through wear: the screen is still intact, so it can quietly pass oversize until a downstream check or a customer finds the problem.
- The gasket seats badly: a poor fit of the seal between the mesh ring and the machine body allows product to bypass the screen altogether, lets dust escape, and creates uneven pressure that accelerates wear on the mesh.
Wear rate depends on the abrasiveness of the material, the mesh construction and aperture used, and throughput. Mesh selection is one of the key variables adjusted during a trial rather than something that can be specified generically. For abrasive applications, agree a realistic replacement interval at the specification stage and build it into the operating budget.
How to decide:
- Align inspection practices with site quality requirements, product risk and operating conditions.
- Check for aperture enlargement as well as for breaks and distortion, since a worn screen passes oversize while appearing serviceable.
- Consider holding spare mesh frames and seals where production continuity is critical.
- Ensure replacement screens are ordered against the correct machine and mesh specification, including aperture and material.
- Confirm that replacement mesh is manufactured and tensioned using a controlled process to ensure consistent performance.
When this advice may not apply: On a low-hours batch machine running a non-abrasive product, inspection at each clean-down is usually sufficient and a scheduled replacement interval adds cost without reducing risk.
Quick reference table: what to record before specifying mesh
| Input | Why it matters | What to record |
| Largest acceptable particle size | Sets the aperture. Specifying from the contaminant instead can produce a mesh that is too coarse or too fine, and a mesh that is too fine reduces yield. | The figure with a tolerance, and how it was measured |
| Separation required | Decides whether one mesh or a graded stack is needed, which decides the machine. | Check sieving, or the number of cuts with upper and lower limits for each |
| Throughput required | Sets the open area and machine size needed to achieve the aperture chosen. | Fines throughput rate in kg/h or t/h, with the oversize percentage |
| Bulk density | A throughput figure quoted without density is not comparable between suppliers. | kg per cubic metre, as delivered to the sieve |
| Moisture and flowability | Turns a workable aperture into a blinding problem. | Moisture at the sieve inlet, not at the dryer outlet |
| Particle shape | Flakes, fibres and elongated particles do not behave as their nominal size suggests. | A note on shape, and whether bars rather than mesh are appropriate |
| Abrasiveness | Sets mesh life, mesh material and the spares budget. | Material and any known wear history from the existing screen |
| Regulatory requirements | Constrains mesh material, surface finish, documentation and cleaning validation. | Standards applying, and whether material certificates are required |
| Line constraints | Decides frame dimensions, headroom for mesh removal and connection types. | Inlet and outlet positions, available height, connection sizes |
Typical mesh sizes, mesh counts and open areas
Typical sizes only. This chart shows just a small fraction of the mesh apertures available and does not cover every possible combination of aperture, wire diameter and material. Many more options can be sourced on request, so if you cannot find the specification you need, Farleygreene can advise on the most suitable and readily available mesh for your application. The values shown are taken from the Farleygreene Mesh Guide (revised October 2026); calculations using the formula above may produce slightly different mesh count and open area figures.
| Aperture (mm) | Mesh count (holes per inch) | Wire diameter (mm) | Open area (%) |
| 0.025 | 510 | 0.025 | 25 |
| 0.050 | 320 | 0.030 | 39 |
| 0.063 | 245 | 0.040 | 38 |
| 0.075 | 230 | 0.036 | 45.7 |
| 0.100 | 169 | 0.050 | 44.4 |
| 0.150 | 102 | 0.100 | 36 |
| 0.200 | 88 | 0.090 | 48 |
| 0.250 | 62 | 0.160 | 38 |
| 0.400 | 41 | 0.220 | 41 |
| 0.500 | 38 | 0.160 | 57.6 |
| 0.600 | 33 | 0.160 | 62.3 |
| 0.630 | 32 | 0.160 | 64 |
| 0.710 | 29 | 0.180 | 64 |
| 0.850 | 24 | 0.200 | 65.5 |
| 0.900 | 23 | 0.200 | 67 |
| 1.000 | 19.2 | 0.320 | 57.6 |
| 1.250 | 15.4 | 0.400 | 57.6 |
| 1.500 | 11.9 | 0.630 | 49.6 |
| 2.000 | 9.9 | 0.560 | 60 |
| 2.500 | 8.5 | 0.500 | 69.4 |
| 3.150 | 6.4 | 0.800 | 64 |
| 4.000 | 5.4 | 0.710 | 72 |
| 5.000 | 3.8 | 1.600 | 57.6 |
| 6.300 | 3.4 | 1.250 | 69.4 |
| 7.100 | 3 | 1.400 | 69.4 |
| 8.000 | 2.6 | 1.600 | 69.4 |
| 10.000 | 2.2 | 1.400 | 77 |
| 12.500 | 1.8 | 1.600 | 79 |
Download the Farleygreene Mesh Guide (PDF)
How to start a mesh enquiry
Replacing mesh on an existing machine? Send the machine serial number, the aperture and the material grade to our aftersales team.
Switching from another supplier? Send photos of the ring or frame with its diameter, plus the aperture and material grade.
Specifying mesh for a new application? Farleygreene can carry out product testing on your product to confirm the right aperture and mesh type before supply.
Use the Remesh Request form for replacement screens, or contact the team to discuss product testing or a new application.
