How is particle size measured? 6 methods for industrial powder analysis
The particle size of industrial powders is usually measured by sieve analysis, air jet sieving, laser diffraction, dynamic image analysis, dynamic light scattering or sedimentation. Laser diffraction (ISO 13320) is the most common method for fine powders; sieving is simple and suits coarser products. The result is often reported as D10, D50 and D90.
Key points
- The right method depends on measuring range, particle shape and purpose
- D50 is the median: half of the volume consists of smaller particles
- Different methods give different results; compare only results from the same method
- Particle size affects flow behaviour, dust formation, segregation and dissolution
- Fine powders require more attention to dust-free handling
6 methods compared
| Method | Indicative range | Strong at | Limitation |
|---|---|---|---|
| Sieve analysis | Coarse, from approx. 20 µm to several mm | Simple, cheap, robust | Slow; less suited to fine or cohesive powders |
| Air jet sieving | Finer than dry sieving | Fine fractions that clump on a sieve | One sieve per measurement |
| Laser diffraction (ISO 13320) | Submicron to millimetres | Fast, reproducible, wide range | Assumes spherical particles |
| Dynamic image analysis (ISO 13322-2) | A few µm to mm | Also measures shape | Less suited to very fine particles |
| Dynamic light scattering (ISO 22412) | Nanometres to a few µm | Nanoparticles in suspension | Liquid only; not for broad distributions |
| Sedimentation | Fine particles | Measures by settling velocity | Depends on density and liquid |
Reading D10, D50 and D90
D10 means 10% of the volume consists of smaller particles, D50 is the median and D90 the size below which 90% falls. The span is (D90 − D10) / D50. A narrow distribution usually flows and mixes more predictably.
Why particle size matters for the process plant
- Flow behaviour: finer powders are often more cohesive and discharge poorly; see dosing systems
- Segregation: large size differences increase the risk; see powder mixing
- Conveying: particle size partly determines whether pneumatic conveying suits; see powder transport
- Dust and explosion safety: fine dust stays airborne longer and is often more ignitable; see ATEX and explosion safety
- Exposure: for toxic substances fine dust increases the importance of containment
Sampling
A measurement is only as good as the sample. Take representative samples and account for segregation in the package. Read safe powder sampling.
Frequently asked questions
Which method is most accurate?
No method is best for everything. Laser diffraction is most common for fine powders; image analysis also gives shape information.
Why do sieve and laser results differ?
They measure different properties: sieving sorts by the smallest cross-section, laser diffraction calculates an equivalent sphere.
Should I measure wet or dry?
Dry measurement is closer to the process; wet measurement breaks up agglomerates better. Choose what fits the question.
Conclusion
Choose the method by range and purpose, and compare only results from the same method. Particle size helps determine how you dose, convey and handle a powder dust-free. Contact us for advice on your product.
Author: Joost van Velzen, Managing Director Hecht Technology B.V. Updated: .