(1) The precision of estimates of soil bulk density from organic matter content, expressed as % loss-on-ignition of dry weight, was examined for eight groups of data collected from surface and sub-surface soils on various sites by different workers. (2) The regression derived by pooling all data for surface soils differed significantly in elevation from its counterpart for sub-surface soils. (3) Regressions for individual groups of data for both surface and sub-surface soils, differed in slope and elevation from their respective overall equations and from each other. (4) For greatest precision in estimating soil bulk-densities, the authors recommend research workers to derive equations for their own research sites rather than to rely on general equations.