This paper describes a methodology for determining the number of nurses required to staff Australia's intensive care unit (ICU) beds. The evidence used is level IV, that is the use of expert panel opinion, and it is the strongest and most accurate attempt yet to describe how Australia's ICU beds should be staffed with nurses. The researchers provide ratios of staffing applicable to a variety of situations that should be of use to ICU managers and hospital administrators. Equally, the broader calculations explaining the national supply and demand needs provide an easy to use approach and explanation suitable to health professionals, health administrators, policy advisors, governments, politicians and the broader community. Limitations of the approach and further recommendations are made to encourage future work in this area. Finally, a strong correlation between the number of available 'open' ICU beds in Australia and the number of nurses actually working in ICU at any given time is well demonstrated using the methodology outlined in this paper. Clarification of scope and terminology: This paper focuses on the nursing requirements of ICUs only; occasionally we use the word critical care nurse--this generally refers to those nurses who have completed a generic critical care nursing course but who, for the purposes of our study, are working in ICUs. Critical care units encompass ICUs but may also encompass recovery room, cardiothoracic units, coronary care, emergency departments and many other environments where critically ill patients are cared for and treated. This paper does not cover the broader scope of critical care units, only ICUs.