Optimal stock level is worked out by AVG(Weekly sales) x AVG(Lead_Time_In_Weeks) 

Where AVG(Weekly sales) is the average weekly consumption of the product and AVG(Lead_Time_In_Weeks) is the average known lead time for the given supplier. Sales spikes are not omitted from average weekly sales, so watch out for standard variation. Selecting this option will order stock to meet this optimal stock level.