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Computer-aided design (CAD) tools are frequently employed to verify the design objectives before the fabrication of an integrated circuit. An important circuit parameter that requires accurate characterization is the power consumption due to the strict constraints on the acceptable power envelope of integrated systems. Circuit simulators typically provide built-in functions to measure the power consumption. However, the accuracy of the measured power is mostly overlooked since the approximations and the methodologies used by the existing built-in power estimation tools are not well documented. The research community tends to assume that the built-in functions provide accurate power figures. This blind-trust in the CAD tools, however, may lead to gross errors in power estimation. A generic methodology to accurately measure the power and energy consumption with the circuit simulators is described in this paper. An equation to calculate the device power consumption based on the different current conduction paths in a MOSFET is presented. An expression for the total power consumption of a complex circuit is derived by explicitly considering the different circuit terminals including the inputs, the outputs, and the body-contacts. Results indicate that the power measurements with the built-in functions of widely used commercial circuit simulators can introduce significant errors in a 65 nm CMOS technology. For deeply scaled nano-CMOS circuits, a conscious power and energy measurement with the proposed explicit methodology is recommended for an accurate pre-fabrication circuit characterization. [ABSTRACT FROM AUTHOR]