Abstract Developing product platforms has been recognized as an effective means to implement mass customization. This paper focuses on the customizability issue of design, that is, to evaluate the cost effectiveness of a design to be customized to meet individual customer needs. A customizability index is proposed to facilitate the analysis of customizability from both the customers and the manufacturer perspectives. It involves two dimensions. One is about the intrinsic nature of a design easy to be customized. The other is regarding the customer-perceived value of customization. The utility theory is introduced to model the customer-perceived value of each individual product feature. Conjoint analysis is introduced to explore customer preference for multiple product features. The customizability index is measured based on the information content metric. Customizability analysis manifests itself through the maximization of customer-perceived value while exploiting the potential of design to be customized specified by optimal customizability indices.