Specific cutting force is a key parameter that is important for estimating cutting forces that occur during machining. This information is important for various applications. The most important application is estimation of the stability limit valid for the specific configuration of the machine tool, tool and workpiece. There are a number of procedures used to predict the specific cutting force through various preliminary tests. This paper focuses on an operational method during milling that allows estimation of the specific cutting force using direct information from the machine tool control system. The specific cutting force is calculated as the ratio between the material removal rate and the power measured on the spindle. The method enables easy in-process identification of the specific cutting force that is valid for the specific workpiece material and the specific cutting edge geometry. The method is demonstrated on practical examples.