This paper attempts to narrow the discrepancy between the promised and actual benefits of the available financial evaluation tools for considering cost/benefit tradeoffs of investment in flexible automation of mass manufacturing systems and the actual benefits. To obtain a deeper insight into flexibility and to give consideration to all possible aspects of user experience and capability, the concepts of potential flexibility and realizable flexibility are introduced. Potential flexibility is classified into four elements and realizable flexibility into 11 elements, and a systematic procedure for quantifying realizable flexibility in monetary terms is proposed. The procedure has been applied to a test case with encouraging results.