Measuring circularity is crucial to identify the status quo, set targets, monitor performance, and take action to pursue circular economy efforts. Regulators increasingly require companies to use and disclose recycled content in new products. However, calculating recycled content from closed loops in products is challenging and, so far, has not yet been implemented sufficiently in existing circularity indicators. Our study's contribution consists of three parts: First, we conducted a literature review of existing indicators. Second, we developed the new Product-oriented Closed-loop Material Indicator (PCMI), which includes a detailed calculation method for a product's closed-loop recycled content. Third, we applied the PCMI in an illustrative case study of recycled steel in cars. We show that the PCMI is comprehensive, versatile, and scalable. Thus, the PCMI provides the foundation to accurately measure the closed-loop recycled content in products, allowing companies and policymakers to steer towards higher levels of circularity.