Connecting particle sphericity and circularity

Sphericity, a measure of how much a particle’s shape deviates from spherical, is useful as a shape factor when characterizing particulate materials. However, particle surface areas, required when determining the sphericity, are very difficult to measure. As a result, the circularity, derivable from microscopic views, is often measured instead and assumed to be equal to the sphericity. This paper shows that the two quantities are generally not equal for simple non-spherical shapes and provides advice on improving the estimation of sphericity from circularity.