text: The particle size of a spherical object can be unambiguously and quantitatively defined by its diameter. However, a typical material object is likely to be irregular in shape and non-spherical. The above quantitative definition of particle size cannot be applied to non-spherical particles. There are several ways of extending the above quantitative definition to apply to non-spherical particles. Existing definitions are based on replacing a given particle with an imaginary sphere that has one of the properties identical with the particle.
  ;Volume-based particle size: Volume-based particle size equals the diameter of the sphere that has the same volume as a given particle. Typically used in sieve analysis, as shape hypothesis (sieve's mesh size as the sphere diameter).
  :where
  ::: diameter of representative sphere
  ::: volume of particle
  ;Area-based particle size: Area-based particle size equals the diameter of the sphere that has the same surface area as a given particle.  Typically used in optical granulometry techniques.
  :where
  ::: diameter of representative sphere
  ::: surface area of particle