A methodology for measuring and predicting work load on nursing units utilizes perceptions of head nurses as measured by a specially designed questionnaire. The data were collected in a 300-bed short-term general hospital over a seven-week period. The results indicated that head nurses' perceptions of need on nursing units were predominantly influenced by unit census and available staff on the unit. Other patient load affecting variables, such as patient classification, number of new admissions, or postoperative patients, did not play a major role in shaping head nurses' perceptions.