Protected Area (PA) managers and policy makers need to determine and demonstrate the effectiveness of PA management and keep track of the conservation status in ways that are practical, scientifically sound and comparable among PAs in various terrestrial and aquatic environments. As most existing methods for measuring the managerial efficiency of PAs are restricted to specific elements of the management or a limited number of detailed environmental aspects, often without the participation of practitioners, we aim for a generally applicable method developed in close cooperation with PA managers; the Protection Level Index (PLI). PLI includes ecological, socio-economic, as well as managerial factors, and consists of twelve variables that together describe the state of a PA. Seven of those are derived from interviews with PA managers, and five of them are derived from GIS analyses. Data were obtained during face-to-face interviews with PA managers using a fixed protocol, thereby introducing a new way of incorporating the perception of the PA managers. PLI was tested in seven different PAs across Europe. The lowest final PLI score was for the Island Network of Protected Areas in La Palma and the highest final PLI score was for the Kalkalpen National Park. PLI is wider applicable than other related methods and more cost-effective. Therefore PLI can be used on a yearly basis to keep track of the progress of management activities and conservation status within and among (networks of) PAs.