The size of a particle is referred to as “grain size,” also known as “particle size” or “diameter.” When a particular physical property or behavior of the particle being measured most closely resembles that of a homogeneous sphere (or a combination of spheres) with a specific diameter, the diameter of that sphere (or the equivalent combination) is taken as the particle’s equivalent grain size (or particle-size distribution). Of course, for non-spherical particles, the reported grain size depends on the measurement reference and the statistical method used; thus, the grain size can only be considered “equivalent.”

The percentage (or cumulative percentage) of particles within each size interval relative to the total powder mass is referred to as the frequency particle-size distribution (or cumulative particle-size distribution). The vertical axis represents the particle-size composition calculated on different bases—such as number, length, area, or volume—expressed as percentages or cumulative percentages, while the horizontal axis denotes the particle-size values computed on the same bases. D10, D50, and D90 can indicate the degree of uniformity of the powder and are also known as the cumulative particle-size distribution.

D50: Also known as the median particle size, it refers to the particle diameter corresponding to a cumulative distribution percentage of 50%. This is a typical value for characterizing particle size; it precisely divides the population into two equal parts—meaning that 50% of the particles have diameters larger than this value, while the other 50% are smaller. For example, if a sample has a D50 of 5 μm, it indicates that among all particles in the sample, 50% are larger than 5 μm and 50% are smaller. D50 is commonly used to represent the average particle size of a powder. D90: This is the particle diameter at which the cumulative distribution reaches 90% when sorted from smallest to largest. In other words, for a given powder, 97% of the particles have diameters smaller than D90. It is typically employed to characterize the coarse‑end particle size and is a key parameter in powder production and applications. Similarly, some industries use values such as D95 or D97, which carry physical meanings analogous to D90. D10: This denotes the particle diameter below which the cumulative percentage is 10%, the opposite of D90. These three parameters are of great significance in both industrial processes and everyday life. For instance, in the pharmaceutical industry, knowledge of a drug’s particle size distribution can inform its efficacy and potential side effects. Likewise, in environmental protection, particle size distribution serves as an important indicator in monitoring air and water quality. In summary, D10, D50, and D90 are three critical parameters in particle size distribution, each reflecting the distribution of particles within specific size ranges. Fine particulate matter finds extensive applications in daily life and industrial production, and its size and distribution directly impact process efficiency, product quality, energy consumption, and operational safety. Therefore, accurate and convenient measurement of particle size (diameter) and derivation of the particle size distribution function are highly valuable.