Energy intensity—calculated as total energy consumption divided by real gross domestic product (GDP)—is a common energy indicator and efficiency measure. In 2020, U.S. energy intensity reached a low of 5.05 thousand British thermal units (Btu) per chained 2012 dollar, down 4% from the previous year and less than half as energy intensive as the United States was in 1983. Energy intensity varies greatly by state, and some states operate with much greater energy intensity than the U.S. average.