Total primary energy requirement (TPER) divided by gross domestic product (GDP) is a commonly used indicator that measures national energy efficiency. However, this indicator is too approximate to represent actual efficiency and is misleading, This paper tries to estimate a ＇real and single＇ indicator that can be used for international comparison of energy intensity directly, A case study between the US and Japan indicates that the US consumes only 23% more energy than Japan, while a comparison using TPER/GDP shows that the US consumes 72% more.