Agricultural production is inseparable from environmental sustainability, and several methods have been developed by numerous authors and organizations worldwide to measure and evaluate it. The aim of the study is to comprehensively and accurately assess the environmental sustainability of farms. Concerning the theoretical framework, a set of 8 indicators and 23 sub-indicators was established to estimate the different aspects of environmental sustainability. The practical compliance of the indicators was assessed based on data from Hungarian agricultural enterprises; an agricultural company and three individual farmers were included in the case studies. By grouping the indicators, a new composite environmental indicator was developed to measure environmental sustainability. The results of the study show that the surveyed farms are moderately sustainable, as their composite indicators were at or close to the minimum of 0.5 points, but none of them were outstanding or at least 0.75 points. More significant efforts should be made to improve the farms’ environmental sustainability in the future.