Equivalent spherical diameter

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In science, the equivalent spherical diameter (or ESD) of an irregularly-shaped object is the diameter of a sphere of equivalent volume.[1]

According to the IUPAC definition,[2] the equivalent diameter of a non-spherical particle is equal to a diameter of a spherical particle that exhibits identical property (e.g., aerodynamic, hydrodynamic, optical, electrical) to that of the investigated non-spherical particle. For particles in non-turbulent motion, the equivalent diameter is identical to the diameter encountered in the Stokes' law.

See also[edit]


  1. ^ Jennings, B. R. and Parslow, K. (1988) Particle Size Measurement: The Equivalent Spherical Diameter. Proceedings of the Royal Society of London. Series A 419, 137-149
  2. ^ Definition of equivalent diameter in the IUPAC goldbook