When the information regarding the prices and quantities of consumption of different items are given

- Laspeyre’s Formula: The base year expenditure p
_{0}q_{0} is assigned as weight of the price relatives \(\frac{p_1}{p_0}\). It is denoted by symbol I_{L}.
- Paasche’s Formula: The expenditure p
_{0}q_{1} of an item is assigned as the weight of the price relatives \(\frac{p_1}{p_0}\). It is denoted by the symbol I_{p}.
- Fisher’s Formula: The geometric mean of Laspeyre’s and Paasche’s index numbers is called Fisher’s index number and it is denoted by the symbol I
_{F}. Fisher’s index number is called an Ideal index number.