d50, d90 and d97 are characteristic particle sizes below which approximately 50%, 90% and 97% of the reported distribution fall on the selected measurement basis. They should always be interpreted together with the measurement method and reporting basis.
What do d50, d90 and d97 describe?
D-values are characteristic sizes on a cumulative particle-size distribution below which the stated percentage of the reported material amount lies. For example, d50 is the size below which approximately half of the distribution lies on the selected reporting basis.
What is the percentage based on?
Depending on the technique and report, the distribution may be volume-, mass- or number-based. Results should not be compared directly across methods unless this basis is stated.
d50: the central characteristic size
d50 is the median characteristic size, not the arithmetic mean. A broad or multimodal distribution cannot be fully described by d50 because the coarse tail and distribution shape remain hidden.
Product d50 and classifier d50 are different contexts
Product d50 describes the cumulative size distribution of one product sample. A classifier cut d50 is derived from how particles of each size divide between streams and represents a characteristic separation point.
d90 and d97: the upper side of the distribution
d90 and d97 cover a larger share of the reported distribution and provide more information about the coarse side than d50. They do not identify the single largest particle or an absolute top size.
Why specify more than one value?
d50 can track the centre of the distribution, while d90 or d97 can help control the coarse tail. Acceptance criteria should reflect end use and measurement uncertainty.
Measurement method and sample preparation
ISO 13320 notes that instrument qualification, measurement conditions and the optical model influence particle-size distributions reported by laser diffraction. Non-spherical particles can give different equivalent sizes when measured by methods based on different physical principles.
Record these items for repeatability
- Measurement technique and instrument method
- Dry or wet dispersion
- Sampling and preparation procedure
- Volume, mass or number basis
- Optical or shape assumptions
- Replicates and quality controls
D-values are not the same as F80/P80
| Term | Context | Meaning |
|---|---|---|
| d50 / d90 / d97 | Cumulative size distribution of a sample | Characteristic size below which the stated share of reported material lies |
| F80 | Grinding-circuit feed | 80% passing size of the feed distribution |
| P80 | Grinding-circuit product | 80% passing size of the product distribution |
| Classifier d50 | Partition behaviour | Characteristic point at which particles divide between streams |
Although the notation uses sizes and percentages, sample distribution, grinding-stream labels and classifier performance answer different engineering questions.
How should a product specification be written?
- Identify the material and sampling point
- State the measurement method and distribution basis
- Define required d50/d90/d97 values in context
- Control sample preparation and dispersion
- Define tolerance and acceptance procedure
- Do not reduce the specification to one generic micron label
This page explains measurement terminology; it does not publish a cut-size or product guarantee for a specific Estilo separator.
Correct use in process design
When feed and product samples are representative and measured consistently, d-values help monitor grinding, classification and product collection. They still need to be read with mass balance, throughput and circuit behaviour.
Product description in the Kütahya reference
The Kütahya Quartz Grinding Plant case study identifies a dry fine quartz product and an integrated process flow. Because the approved publication source contains no characteristic d50, d90 or d97 value, the project is not assigned a numeric D-value or separator cut size.
