Average tidal prism volumes have been calculated for 51 estuaries in NSW with tidal gauging data on flood and ebb tide velocities and flows. Various corrections were made to the tidal gauging data, which are generally collected on a spring tide and upstream of the entrance, to enable calculation of an average tidal prism. Data on estuary surface area was used to calculate an average tidal range.; ; Tidal ranges for estuaries were estimated to support the development of a new response-based estuary classification system based on dilution and flushing characteristics. The classification system was used to stratify estuaries in NSW for the development of reference conditions and the design of a sampling program of chlorophyll a, turbidity and associated water quality parameters to assess estuary health.