A practical method for estimating the shear strength of rockfill is developed. The peak drained friction angle π(prime) is found to be closely related to that of rock joints. In both cases the values of π(prime) are dependent on sample size, stress level, surface roughness, and on the uniaxial compression strength of the rock. Friction angles are therefore higher for smaller samples, and very high where stresses are low, as at the toe or near the face of a rockfill dam. Test data reviewed shows that the value of π(prime) for rockfill can be quantified by a equivalent roughness (R), and an equivalent particle strength (S). The value of (R) depends on the porosity following compaction, and on the degree of particle roundedness and surface smoothness. A practical method is proposed for physically measuring the full-scale shear strength of in-place compacted rockfill.