There is an increasing need to reuse existing legacy software systems within the context of a modern software architecture. There are two ways to achieve this, either by re‐engineering or by wrapping. In this paper a pair of metrics are discussed for deciding whether a program is reusable at all, and if so, whether to convert it or to wrap it. Managers should be aware of both alternatives and be able to decide which alternative is best suited for them. The metrics proposed in this paper are intended to support this decision making. The metrics have emerged from the experience of the author in conducting re‐engineering and wrapping projects in the last ten years. Copyright © 1998 John Wiley & Sons, Ltd.