When power consumption in smartphones becomes much higher, several significant impacts occur due to its small form factor, such as performance degradation and worse user experience. Thus, power estimation/mapping is essential and useful for dynamic power management and power model validation for smartphones. In this work, first, we build the power-to-temperature (P-to-T) equations for thermal sensors from the existing system-level thermal model and calibrate them using the least squares fitting. Furthermore, we develop an efficient method for the temperature-to-power (T-to-P) mapping, which obtains the power consumption of components by utilizing temperatures of thermal sensors. Experiments show that this work can estimate power profile efficiently for both steady-state and transient results.