Sphericity

Sphericity is a measure of how spherical (round) an object is. As such, it is a specific example of a compactness measure of a shape. Defined by Wadell in 1935, the sphericity, ${\displaystyle \Psi }$, of a particle is: the ratio of the surface area of a sphere (with the same volume as the given particle) to the surface area of the particle:

where ${\displaystyle V_{p}}$ is volume of the particle and ${\displaystyle A_{p}}$ is the surface area of the particle. The sphericity of a sphere is unity by definition and, by the isoperimetric inequality, any particle which is not a sphere will have sphericity less than 1.

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