Dielectric elastomer actuators (DEAs) have raised interest in the field of mobile robotics. In such a field, actuator design requires a fundamental understanding of DEA energy conversion performance. To provide insight into DEA mechanical work, energy consumption, and efficiency, this paper proposes a simple thermodynamic description completed by experimental loss factors obtained over a broad range of operating conditions and modes. Extensive data gathered on cone actuators show practical efficiency limits of ~ 26% for acrylic actuators (VHB 4905) operating under constant charge mode and ~ 18% for silicone actuators operating under constant voltage mode. While charge recovery could raise these limits to ~ 60%, the study of a DEA rotary motor shows significant efficiency degradation caused by unconstrained electrode boundaries.