Extensive data of the strength and dilatancy of 17 sands in axisymmetric or plane strain at different densities and confining pressures are collated. The critical state angle of shearing resistance of soil which is shearing at constant volume is principally a function of mineralogy and can readily be determined experimentally within a margin of about lo, being roughly 33^o for quartz and 40^o for feldspar. The extra angle of shearing of ‘dense’ soil is correlated to its rate of dilation and thence to its relative density and mean effective stress, combined in a new relative dilatancy index. The data of φ_max-φ_crit, in triaxial or plane strain are separately fitted within a typical margin of about 2^o, though the strength of certain sands is underpredicted in the 1000-10000 kN/m² range owing to the continued dilation of their crush-resistant grains. The practical consequences of these new correlations are assessed, with regard to both laboratory and field testing procedures.