In order to calculate/measure the fundamental harmonic power values, the wavelet transform based methods have been proposed in the literature. However, the fundamental harmonic of voltage and cur-rent signals cannot be decomposed into real and imaginary components in any of these methods based on only wavelet packet transform. It is required to decompose voltage and current signals with harmonics to real and imaginary components in a power system for power quality and control. In this study real and imaginary components are obtained by using the wavelet packet transform. Furthermore, the fundamental active-reactive-apparent powers are determined with two different methods and accurateness of the proposed methods is demonstrated via simulations.