particle size; grain size; granularity
Technical term used in materials science, geology, and engineering to describe the size of particles or grains in a substance. Also used metaphorically in computing for the level of detail or resolution.
The grain size of this sand is very fine.
Increasing the granularity of the data allows for more detailed analysis.
particle size distribution
Compound of 粒 (りゅう, 'grain, particle') and 度 (ど, 'degree, measure'). The meaning is transparent from its components.