With recent advances on mobile computing, power consumption has become a significant limiting constraint for many graphics applications. As a result, rendering on a power budget arises as an emerging demand. In this paper, we present a real-time, power-optimal rendering framework to address this problem, by finding the optimal rendering settings that minimize power consumption while maximizing visual quality. We first introduce a novel power-error, multi-objective cost space, and formally formulate power saving as an optimization problem. Then, we develop a two-step algorithm to efficiently explore the vast power-error space and leverage optimal Pareto frontiers at runtime. Finally, we show that our rendering framework can be generalized across different platforms, desktop PC or mobile device, by demonstrating its performance on our own OpenGL rendering framework, as well as the commercially available Unreal Engine.