GDP is used to measure economic growth and compare economic well-being over time and across countries. Real GDP measures the value of final goods and services produced adjusted for inflation. It is calculated using the chained-weighted output index method, which values one year's output using the previous year's prices and the current year's prices. While real GDP provides useful information, it does not perfectly measure economic welfare due to factors like quality improvements, household production, and environmental costs that are excluded from its calculation.