In the present work a semiempirical method for characterizing the electronic density of pure metals (or, equivalently, the mean radius, r(s), per electron) from the bulk modulus is proposed. The general features of this method are discussed and shown to be simple and useful for many situations. Knowledge of r(s) is important because it determines several important properties of the metal. For instance, the interaction with a hydrogen impurity is dominated by the interstitial electron density, and we check the applicability of the obtained values of r(s) by evaluating the volume of solution of hydrogen in pure metals. Our results are in excellent agreement with the available experimental data.