Radius of gyration (K): The radius of gyration of a given area about any axis is the distance from the given axis at which the area is assumed to be concentrated without changing the MI about the given axis.

$$ K=\sqrt{\frac{I}{A}} $$

$$ \begin{aligned} \text { Where, } I &=\text { Moment of Inertia }\left(\mathrm{mm}^{4}\right) \\ \mathrm{A} &=\text { Cross Sectional Area }\left(\mathrm{mm}^{2}\right) \\ \mathrm{K} &=\text { Radius of Gyration. (mm) } \end{aligned} $$

Sectional Modulus (Z): It is the ratio of moment of inertia to the distance of extreme fiber from neutral axis.

$$ \begin{array}{c}{Z=\frac{I}{Y}} \\ {\text { Where, } Z=\text { Section Modulus }\left(\mathrm{mm}^{3}\right)} \\ {\mathrm{I}=\text { Moment of Inertia }\left(\mathrm{mm}^{3}\right)} \\ {\mathrm{Y}=\text { Distance of neutral axis from top or bottom (mm) }}\end{array} $$