PT. ETB is a world-class electronics manufacturing company located in Batam Island. Inventory control becomes one of the obstacles faced by management. The values of the inventory is very high but have not been able to increase the service level to be a problem that must be resolved. This study will analyze the performance of inventory and calculate optimal inventory value in order to achieve better service levels at optimum cost. Design methods of this study was observational analytic is to determine performance assessment of the Inventory for Trigger Coil product to support service level to customers (Service Level) Results from this study showed that the performance of inventory in 2012 is not yet optimal. This can be seen from the costs incurred to bring inventories such as a set up cost and holding costs amounted to $ 28,838, while when using Wagner Whitin method of the cost of $ 17,130 and there is a potential savings of $ 23,416 / year. In addition, Min Max and ROP values obtained from the calculation will help companies improve the effectiveness of inventory and service levels to the customer (service level). This study also provided recommendations and some suggestions for improvements to the Management to improve service levels to customers while reducing unnecessary costs Keywords: Wagner Whitin, Service Level, Inventory Level, Set up cost, Holding Cost, Min Max