Radius of Gyration (K)
The radius of gyration of given lamina about given axis is that distance from te given axis at which all the elemental parts of lamina would have to be placed so as not to change the moment of inertia about given axis.
K = (I/A)1/2
Kxx = (Ixx/A)1/2
Kyy = (Iyy/A)1/2
Kxx = Radius of gyration of area from x-x axis
Kyy = Radius of gyration of area from y-y axis