The measurement of the integral, with respect to time, of the power in an electric circuit. The absolute unit of measurement of electrical energy is the joule, or the charge in coulombs times the potential difference in volts. The joule, however, is too small (1 watt-second) for commercial use, and the more commonly used unit is the watt-hour (3.6×10³ joules). The most common measurement application is in the utility field.