Single uncharged pion production in neutron- and proton-induced reactions on complex nuclei, combined with the nuclear Fermi Gas Model, has been used to evaluate the average equivalent radius of a [Formula: see text] nucleus directly from the experimental nuclear mass-values of [Formula: see text] and its neighbors [Formula: see text] and [Formula: see text] isobars. A simple formula without adjustable parameters has been derived which gives nuclear radius-values that are in good agreement with updated, equivalent root-mean-square (rms) radius-values derived from experiments for a set of 540 nuclides comprising spherical, quasi-spherical, stable and long-term half-life nuclides. We shall call by RFNM-approach the present method of nuclear radius determination.