Precision density measurements on dilute hydrides deuterides and tritides of V, Nb and Ta are presented. From the essentially linear decrease of the density with solute content. Values are obtained for the lattice expansion ( Delta nu / Omega )_i for each hydrogen isotope. The data strongly suggest a small decrease of ( Delta nu / Omega ) when going from H to D. The tritium values are close to those for H and D, but are less precise. The accuracy of the present density derived data set represents a considerable improvement over previous lattice parameter derived values for the lattice expansion.