The potential benefits of software reuse motivate the use of component based software development and software product lines. In these software development methodologies software assets are being reused. Variability management is a tenet of software reuse. Variability is the capacity of software to satisfy variant requirements. Variability, being the central player in reuse and an important characteristic of reusable components, needs to be measured. In this paper we acknowledge this need and identify measures of variability. Variability implementation mechanisms are analyzed followed by metrics. The metrics are applied on open source component code and the results are validated by an experiment carried out with human subjects. © 2011 Springer-Verlag.