Micron and Mesh Conversion Guide
Convert between micron, mesh and inches, and match the filtration degree to what you're protecting downstream.
Why the filtration degree matters
Filtration degree is the finest particle size a screen or mesh will reliably remove, expressed in microns (µm) or mesh count. Get it wrong in either direction and the cost shows up somewhere else in the system.
Too coarse, and solids pass through to foul heat exchangers, block spray nozzles, or shorten membrane life. Too fine, and pressure drop climbs, backwash frequency increases, and the filter does more work than the application needs.
Mesh count and micron rating aren't the same measurement — mesh counts openings per linear inch, while micron rates the actual opening size. The two only line up consistently once wire diameter is fixed, which is why the conversion is a reference table, not a formula you can do in your head.
Micron to mesh conversion
Standard US mesh sieve series (ASTM E11) reference values.
| Micron (µm) | Millimetres (mm) | US Mesh (approx.) | Inches |
|---|---|---|---|
| 30 | 0.030 | ≈450 | 0.0012 |
| 50 | 0.050 | ≈270 | 0.0020 |
| 75 | 0.075 | 200 | 0.0030 |
| 100 | 0.100 | ≈140 | 0.0039 |
| 125 | 0.125 | 120 | 0.0049 |
| 150 | 0.150 | 100 | 0.0059 |
| 200 | 0.200 | ≈70 | 0.0079 |
| 250 | 0.250 | 60 | 0.0098 |
| 300 | 0.300 | 50 | 0.0118 |
| 425 | 0.425 | 40 | 0.0167 |
| 500 | 0.500 | 35 | 0.0197 |
| 600 | 0.600 | 30 | 0.0236 |
| 800 | 0.800 | ≈20 | 0.0315 |
| 1000 | 1.000 | 18 | 0.0394 |
| 1500 | 1.500 | ≈14 | 0.0591 |
| 2000 | 2.000 | 10 | 0.0787 |
| 3000 | 3.000 | ≈7 | 0.1181 |
How to select a filtration degree
Work through these checks in order — each one narrows the practical range before the next.
- 1
Identify the smallest downstream clearance
Nozzle orifice, membrane spacer, heat exchanger tube gap, or valve seat — the tightest tolerance in the system sets the ceiling on particle size you can allow through.
- 2
Apply a safety margin
A common starting rule is filtering to roughly a third to a fifth of the smallest clearance, so normal variation in particle shape and orifice wear doesn't let solids through.
- 3
Check the water source
Bore water, recycled water and open cooling circuits carry different solids loading. A finer degree on a dirty source increases backwash frequency — confirm the source before locking in a rating.
- 4
Balance against flow rate and pressure drop
Finer screens have less open area for the same size, which raises pressure drop at a given flow rate. Confirm the selected degree still meets the required flow at an acceptable pressure loss.
- 5
Confirm with the equipment being protected
Where a membrane, chiller or nozzle manufacturer specifies a maximum inlet particle size, that figure overrides the general guidance above.
Typical starting points by application
Conservative reference values — confirm against your specific equipment tolerances and water source.
| Application | Typical starting point | Mesh equivalent |
|---|---|---|
| Cooling tower / heat exchanger protection | 150-200 micron | ≈100–70 mesh |
| Spray nozzle protection (irrigation, dust suppression) | 100-200 micron | ≈140–70 mesh |
| RO / UF membrane pre-filtration | 25-100 micron | ≈500–140 mesh |
| Process make-up water / general plant water | 100-150 micron | ≈140–100 mesh |
| Drip irrigation emitters | 120-150 micron | ≈120–100 mesh |
| Seawater or river intake, coarse pre-filtration | 200-500 micron | ≈70–35 mesh |
Confirm the right filtration degree for your system
The configurator sizes a filter to your flow rate, pressure and application, including the recommended screen degree.