In component-based software development, it is necessary to measure the reusability of components in order to realize the reuse of components effectively. There are some product metrics for measuring the reusability of object-oriented software. However, in application development with reuse, it is difficult to use conventional metrics because the source codes of components cannot be obtained, and these metrics require analysis of source codes. We propose a metrics suite for measuring the reusability of such black-box components based on limited information that can be obtained from the outside of components without any source codes. We define five metrics for measuring a component's understandability, adaptability, and portability, with confidence intervals that were set by statistical analysis of a number of JavaBeans components. Moreover, we provide a reusability metric by combining these metrics based on a reusability model. As a result of evaluation experiments, it is found that our metrics can effectively identify black-box components with high reusability.