To narrow the discrepancy between the benefits of investment in flexible automation of manufacturing systems promised by financial evaluation tools and the benefits realized in practice, we distinguish the potential flexibility of a system from its realizable flexibility. A classification is given of the realizable flexibility in automated manufacturing systems in mass, mid-variety and mid-volume, and multi-variety and small-volume production systems. A systematic procedure for quantifying the realizable flexibility in monetary terms and integrating this value into a Financial evaluation model is proposed and applied to a test case with significant results. Comparisons are also made with typical previous studies.