This paper proposes a method for estimating the feed base, grazing pressure and variability as an indicator of risk in grazing lands. Together, they may be considered as surrogate measures of biophysical sustainability. The paper applies them to four transects, each from unfertilised rangeland to relatively intensive mixed farming in temperate Australia. Across the transects, the feed base, stocking rates and grazing pressure in 1987-97 increased with increasing median annual rainfall, and grazing pressure decreased with increasing inter-year variability in the feed base. Average year-round grazing pressures generally ranged from 0.2 to 0.3-0.5. Periods of critical grazing pressure, defined as times when the calculated feed base fell below some critical value, say 0.7 t ha-1, decreased markedly with increasing rainfall and decreasing variability in the feed base. Long periods of critical grazing pressure in areas receiving less than 400 mm rainfall suggests grazing practices may be unsustainable. Stocking rate and annual average grazing pressure (with or without account for feral animals) did not appear to be, in themselves, good indicators of sustainability. Rather, the sustainability of different areas/systems and the impacts on sustainability of changes in management, e.g. stocking rates, may be assessed better through calculating year-to-year variability of the feed base, and periods of critical grazing pressure.