Inflation is typically measured using a consumer price index that tracks the change in the overall cost of a representative basket of goods and services purchased by households. The basket contains many items covering categories such as food, clothing, transport, housing-related costs, recreation, and services. Each item is weighted to reflect its importance in average household spending, so the index measures the cost of living in a broad, systematic way. Central banks use this measure, or a closely related headline or core version, as the primary inflation gauge when setting monetary policy. A survey of banks may inform market expectations, but it is not how inflation is calculated. Changes in interest rates can influence inflation, but they are not the measurement basis. Commodity prices are relevant because they can feed into consumer prices, yet inflation is not calculated from commodities alone; it is derived from the overall consumer basket. The exam point is that inflation is an index-based measure built from a basket approach with weightings, reviewed periodically to reflect changing consumption patterns.