For true optimum operation of reorder level policy of invetory control, reorder levels and replenishment order quantities must be calculated jointly. This is because the size of one quantity directly influences the size of the other in the overall reorder level inventory situation - Assuming that demand per unit time is distributed normally and leadtime is constant. From normal distribution table, as approximate relation between percentage probability (F) of stockout and a sefty stock of (k) standard deviation of demand during the leadtime is given. Using this relation in the total cost equation to calculate the stock-out term, we can get a direct value for replenishment order quantity and reorder level quantity which ensure the minimum COST required for optimum policy - An example is given to prove that this method proves the optimum solution rather that the one of separate calculation of the two parameters of this policy .