An economic measure calculated as the average change in prices for a fixed group (basket) of products and services considered to be either essential or universally desirable for a given population or segment of the population.

The US Bureau of Labor Statistics publishes two CPIs each month for two population groups. The CPI-U is the CPI for urban consumers, and covers approximately 80 percent of the total US population. The CPI-W measures the cost of products and services typically needed by urban wage earners and clerical workers. The CPI-W covers 32 percent of the total population, not 20 percent, because a wage earner can also be a consumer.

The CPI is considered a key indicator of economic health in the US and is frequently used as a benchmark for both investment and legislative decision-making. Note that the CPI doesn't measure the actual cost of goods and services for the group that it covers. Instead it measures the degree of change in those costs over time.