The rising demand for customized products induces complex changes in the production system and supply chain of manufacturing and services companies. While variety appears essential to satisfy the customer requirements, it cannot be achieved without flexibility, which is part of performance. Dealing with a mass customization strategy, company managers need tools to help them make decisions. This paper proposes a decision support tool, designed for companies oriented toward mass customization, which links the four key concepts: variety, flexibility, performance and customer satisfaction. Designed in the form of an influence diagram, it highlights the main connections between the key metrics involved in mass customization.