During the last decades, vibrations-based piezoelectric energy scavenging has been widely investigated as a way to replace or complement batteries to power sensor nodes in closed and confined environments. Piezoelectric ceramics exhibit conductive and dielectric losses. However, in most models used in energy harvesting, these losses are disregarded, as they appear to be relatively small in manufacturer datasheets. In this paper, after briefly introducing the origins of those losses, we experimentally prove that they are strongly dependent on the electric field in the material. This means that the datasheets data, obtained under low electric field characterizations, are not representative of the actual material losses under real-world vibrations. Thereafter, we prove that these losses limit the harvesting energy bandwidth, and we deduce the theoretical performance boundaries of piezoelectric harvesters. Finally, we study how harvesting energy on a linear resistive load is impacted by the losses in the piezoelectric material. Experimental results are in good agreement with our analysis and show that these losses should be taken into account in the electromechanical models in order to accurately predict the harvestable power from a linear piezoelectric harvester. Copyright © 2018 American Scientific Publishers All rights reserved.