How is particle size determined?

For 3D non-spherical or non-cubic particles, more than one parameter is required to define dimension. You can select a few dimensional numbers to describe a particle for regularly-shaped objects such as a rectangle (2- or 3-dimensional numbers) or cylinder (2-dimensional numbers). For irregular particles however, dimensions can’t be described with a few parameters and when working with millions of particles, describing them individually isn’t practical. Only one number should be used to characterize each particle and this number is size. The definition used to define size will affect the data obtained.

The most common size definition used to describe irregularly-shaped 3D particles is equivalent spherical representation. When using only one value (e.g., diameter) to describe size, all the dimensional information is condensed into a single number and will contain distorted or summarized information about the particle due to its shape.