We aimed to evaluate the effectiveness of a nursing care classification system for re-assessing nurse workload and determining staffing needs. Adequate bed–nurse ratios help manage hospital cost-efficiency, quality of care and patient safety. A prospective pre-post intervention study was conducted from January 2010 to December 2012 in 16 medical-surgical units of a tertiary teaching hospital. Nursing tasks were classified into four grades of care reflecting actual workload. Units were re-staffed accordingly and bed–nurse ratios compared with government-authorized bed–nurse ratios. Patient satisfaction, hospital stays and mortality were evaluated pre- and poststaffing changes. Average bed–nurse ratio (1:0.41) exceeded the national standard (1:0.40) in 16 units, but was inadequate in five units. Re-staffing increased average bed–nurse ratio from 1:0.41 to 1:0.48. Patients' satisfaction increased from 96.9% to 97.6%, and hospital stays decreased significantly. Nursing care classification effectively distributes nurse staffing to match patients' care levels, improving patient outcomes.