This article deals with the problems of electricity metering under non-sinusoidal loads that consume non-sinusoidal currents from network and/or generate distortions into the network. The equations for determination of estimated values of active and reactive electric energy under the presence of higher harmonics are deduced. It is shown and experimentally confirmed that the meters of active and reactive power have unaccounted inaccuracies, which can exceed allowable metrological ranges. Frequency characteristics of some meters, used in the power grids of the Slovak Republic, are received, and they confirm the conducted theoretical studying.