An increasing number of manufacturing companies acknowledge the importance of flow efficiency. As an important key performance indicator in lean implementation processes, being able to measure the throughput time of products is important to assess the current situation. This paper presents a stepwise method for measuring the throughput time in manufacturing environments with no unique identification of products, products made up of several levels of subcomponents, as well as varying batch sizes throughout the process. With relatively few data points, the method calculates the average throughput time of products for a chosen time period. The method is applied to a case company who manufactures wood components.