Conventional wisdom holds that in order to launch a startup, founders identify an entrepreneurial opportunity, write a detailed business plan and execute according to it (Blank, 2013b). Unfortunately, as a result of entrepreneurship’s inherent conditions of high uncertainty (McMullen & Shepherd, 2006), this process often reveals its limitations, when founders realize, that while having perfectly executed their business plan, they built a product that nobody needs (Ries, 2011). As an alternative to the linear approach of business planning, the Lean Startup methodology (LSM) suggests to follow a hypothesis-driven approach to adaptively and iteratively develop a business model (Eisenmann et al., 2011; Blank, 2013a; Maurya, 2012). From a research perspective, LSM is still in a nascent stage. Current authors have laid an initial foundation by articulating the methodology and at this point it is widely acknowledged that applying LSM is beneficial for dealing with conditions of high uncertainty (Blank, 2013a; Fisher, 2012). However, no scale has yet been developed to measure the degree of leanness of a startup, an essential component to empirically validate fundamental relationships and assumptions.