'a' items represent 20% in terms of quantity and 75 to 80% in terms of the value, popularly known as the "80/20" rule. ABC concept is applied to inventory management as a rule-of-thumb. 10-20% of the items ('A' class) account for 70-80% of the consumption the next 15-25% ('B' class) account for 10-20% of the consumption and the balance 65-75%('C' class) account for 5-10% of the consumption