Aim: To measure nurse staffing ratios in critical care and med-surgical units in public hospitals in Chile and to analyze the gap between them and ministerial standards. To assess patient complexity and to examine alignment to beds' complexity definition and staffing. Methods: Multicenter, cross-sectional study. Population: high-complexity public hospitals, with more than 150 beds (n = 48) and bed-side registered nurses working in adult and pediatric critical care or med-surgical units (n = 6,086). No sampling methods were needed. Main variables: nurse staffing ratios, measured through an online nurse survey, and patient complexity, measured through the CUDYR instrument that assesses patients' risk and self-sufficiency. Descriptive and comparative analyses, as per type of variable. Results: Hospitals' response rate 85% (n = 41) and nurses' response rate 68% (n = 4,146). Unequal staffing ratios between hospitals. Mean patients-per-nurse, day shift, adult / pediatric units: ICU 2.9 / 2,6, step-down 4.9 / 5,5, med-surgical 9,6 / 7,7. Mean patients-per-nurse, might shift, adult / pediatric units: ICU 2,9 / 2,5, step-down 4,8 / 6,4, med-surgical 10,6 / 7,3. Low adherence to day-shift ministerial staffing recommendations. Eighty percent of patients occupying "basic level of care" beds, and 30% of patients occupying "medium level of care" beds are more complex than what would be expected for those beds. Conclusions: There is a gap between hospital registered nurse staffing ratios and ministerial recommendations and between patient complexity and bed complexity definitions. There is a need to update ministerial staffing standards, to redistribute hospital beds based on complexity, and to adjust staffing ratios to the new distribution.