Quantum-dot cellular automata (QCA) is a new paradigm in nanoelectronics, where binary information is represented by charge configuration in cells. Ideal QCA logic gates are thought to be dissipationless, since there is no intercell charge transfer and no current flows out of cells. This work presents that these gates dissipate energy and compare energy consumptions of conventional QCA logic gates in electrostatic and thermodynamic approaches. The results show that increasing the number of inputs, concentration of the geometry and the unbalanced numbers of ‘0’ and ‘1’ output states in the gate's truth table add to the energy dissipation of a QCA gate.