Two ways to quantify the shape of particles is the shape index, and the aspect ratio. Shape index relates the particles surface area to the particles volume, and compares that to a sphere, which has the lowest shape index. Aspect ratio is the ratio between a powder particle's greatest dimension and its smallest. A perfect sphere will have an aspect ratio of 1, a rounded particle may have an aspect ratio of 1.5, while acicular or flakey particles may easily have a ratios of 3, 5 or 10.