What Is Mesh Size?
Mesh size is a measure of particle size based on the number of openings per linear inch in a standard test sieve. A -200 mesh powder has particles that pass through a sieve with 200 openings per inch, meaning all particles are smaller than 75 microns (µm). The minus sign indicates the powder passes through the sieve. Higher mesh numbers mean finer powder.
When you see a metal powder specified as "-200 mesh" or "-325 mesh," it's describing the maximum particle size in the sample using a standardised sieve classification system. The mesh number corresponds to a specific sieve in the ASTM E11 standard series, and the minus sign tells you the powder has been screened through that sieve.
This system has been the standard method for classifying metal powder particle size for decades. While laser diffraction and other modern techniques exist, mesh size remains the primary specification language across the metal powder industry, particularly for copper powder, tin powder, bronze powder, and other non-ferrous metals used in diamond tooling, brazing, and powder metallurgy.
How Mesh Converts to Microns
Mesh size converts to microns based on the physical opening size of each standard sieve. Common conversions: -60 mesh = below 250 µm, -100 mesh = below 150 µm, -200 mesh = below 75 µm, -325 mesh = below 45 µm, -400 mesh = below 38 µm. The relationship is not linear, each step corresponds to a specific sieve in the ASTM E11 series.
The conversion between mesh and microns isn't a simple formula, it's based on the physical dimensions of standardised test sieves. Each mesh number corresponds to a specific wire diameter and opening size defined by ASTM E11. Here is the complete reference table for mesh sizes commonly used in the metal powder industry:
| Mesh Size | Microns (µm) | Millimetres | Inches |
|---|---|---|---|
| -40 | < 420 µm | 0.420 mm | 0.0165" |
| -60 | < 250 µm | 0.250 mm | 0.0098" |
| -80 | < 180 µm | 0.180 mm | 0.0070" |
| -100 | < 150 µm | 0.150 mm | 0.0059" |
| -150 | < 106 µm | 0.106 mm | 0.0041" |
| -200 | < 75 µm | 0.075 mm | 0.0029" |
| -250 | < 63 µm | 0.063 mm | 0.0025" |
| -325 | < 45 µm | 0.045 mm | 0.0017" |
| -400 | < 38 µm | 0.038 mm | 0.0015" |
The two most commonly specified sizes across industrial applications, -200 mesh and -325 mesh, are highlighted above. If you're unsure which size you need, our mesh-to-micron converter tool provides instant conversion for any standard mesh size.
What Does the Minus Sign Mean?
The minus sign in mesh sizes (e.g. -200 mesh) means the powder passes through that sieve, so all particles are smaller than the sieve opening. A plus sign (+200 mesh) means the powder is retained on the sieve, particles are larger than the opening. A range like -100/+200 means particles that pass through 100 mesh but are retained on 200 mesh, between 75 and 150 µm.
This is the single most important thing to understand about mesh notation. When you see a specification like "-200 mesh copper powder," it means every particle in the sample has passed through a 200-mesh sieve with 75 µm openings. The powder is finer than 75 microns.
Conversely, "+200 mesh" would mean the powder was retained on the sieve, the particles are larger than 75 microns. And when you see a range like "-100/+200 mesh," it describes a band: particles that pass through 100 mesh (smaller than 150 µm) but sit on top of 200 mesh (larger than 75 µm). This gives you a controlled particle size distribution between 75 and 150 microns.
Why Mesh Size Matters for Your Application
Particle size directly affects how a metal powder behaves in manufacturing. Finer powders (higher mesh numbers) generally provide better surface finish, more uniform sintering, and tighter dimensional control, but they can be harder to handle, more prone to oxidation, and more expensive to produce.
Diamond Tooling
Diamond tool bond matrices typically use -200 mesh to -325 mesh copper and tin powders. Finer particles provide more uniform sintering and better diamond retention in the matrix. The powder morphology, dendritic, spherical, or irregular, matters just as much as size. See our guide: Powder Selection for Diamond Tool Bond Matrices.
Brazing & Soldering
Brazing pastes and compounds typically require -325 mesh or finer powders for consistent paste rheology and uniform melting behaviour. Coarser powders can create uneven joint fill. Read more: Metal Powders for Brazing & Soldering.
Additive Manufacturing
Metal AM processes (SLM, EBM, binder jetting) often require tightly controlled PSD within specific ranges, for example, 15–45 µm for laser powder bed fusion. Mesh classification alone may not be sufficient; laser diffraction analysis is often required alongside sieve data.
Key Takeaway.
Mesh size is the primary language for specifying metal powder particle size. Understanding the conversion to microns, and what the minus sign means, is essential for selecting the right powder grade for your application. If in doubt, speak to our technical team, we've been helping engineers specify metal powders since 1945.
Mesh vs. Micron: Which Should You Use?
Mesh and microns both describe particle size but use different measurement systems. Mesh is based on sieve openings per inch and is the traditional standard in the metal powder industry. Microns (µm) directly measure particle diameter and are used in laser diffraction analysis. Most metal powder specifications use mesh, but modern quality control often reports both mesh and micron (D50, D90) values.
In practice, most metal powder data sheets will specify the primary grade in mesh (e.g. "-200 mesh electrolytic copper powder") and may also include particle size distribution data in microns from laser diffraction analysis. When ordering from Ronald Britton, you can specify in either system, our technical team will ensure the right grade is matched to your requirements.