Open source software foundations and communities often want to know the impact of their software. This impact can be understood in a variety of ways and in this paper we explore impact through the interdependencies of open source software. In this, open source software is dependent on components created upstream and open source software is used in components downstream - impact within an open source supply chain. This paper proposes an index (called the V-index) through which impact of an open source software, as used in downstream components, can be measured. This index is developed using the open database libraires.io, which provides the dependencies of open source software distributed through various package managers. The proposed index helps measure the impact of an open source software as part of its use within an open source supply chain.