For a flexible macromolecule composed of \(n\) mass elements, of masses \(m_{i}\) , \(i = 1, 2, \ldots, n\), located at statistical-mechanical mean-square distances \(\lt\!s_{i}^{2}\!\gt\) from the centre of mass, the mean-square radius of gyration is the mass average of \(\lt\!s_{i}^{2}\!\gt\) over all mass elements, i.e., \[\lt\!s^{2}\!\gt = \left(\sum\limits_{i=1}^{n} m_{i} \lt\!s_{i}^{2}\!\gt\!/\sum\limits_{i=1}^{n} m_{i} \right)\]