What is circularity?

Circularity is how close the particle projection is to a circle. Circularity is calculated by multiplying the projected area by 4π divided by the square of the circumference, and taking the square root. The formula can be expressed as: e=(4π*area)/(circumference*circumference), e is circularity. When e=1, the particle is circular, and the smaller e is, the greater the gap between the particle and the circular shape. For example: the circularity of a circle is 1.0, the circularity of a square is π/4, which is about 0.89, and the circularity of an equilateral triangle is (π*3)/9, which is about 0.78.