In uncertain environments, increased flexibility is necessary to facilitate the development of fast adaptation capability that lead to an effective environmental response. Manufacturing companies generally have some problems about coping with the uncertainty in their industries and they tend to increase the flexibility level of their manufacturing system. Measurement of flexibility is required for this purpose. This paper intends to develop an entropy based model to measure flexibility. The model proposed includes manufacturing characteristics such as type of machinery, number and type of operations, routing for each product as well as time spend for operations, machine set up activities and material handling. An application of the model is performed in a job shop. Flexibility level is measured and the association between the total entropy value and flexibility level is discussed.