[en] We derive inequalities between the radii and kinetic energies of quarkonium states and the values of the wave functions of these states at the origin. Using the Van-Royen-Weisskopf formula to determine the latter quantitiy from leptonic decay widths, we obtain an upper bound on the mass differences between the c quark and b quark in terms of experimental data from the J/psi and γ systems. These bounds improve on those obtained without the use of the information from the decay widths, even when relativistic and gluon-exchange corrections to the Van Royen-Weisskopf formula are taken into account. Similar improvements are made for the lower bounds to the mass of toponium as a function of the top quark mass. (orig.)