A dimmable light-emitting-diode (LED) driver with precise power metering is proposed in this paper. A buck-type power factor corrector (PFC) circuit with the merits of high power efficiency and high power factor (PF) is adapted in the LED driver. The input power of the LED driver can be evaluated precisely by calculating the sensed voltage and current on the output terminal of the PFC circuit. The slight reduction of the power efficiency during dimming can eliminate the error of the power evaluation. Therefore, the electrical sensors of the feedback circuit and the computation algorithm for power evaluation can be simplified to meet the requirements of high accuracy and cost-effectiveness. The detailed design topology, evaluation method, and verification results are provided. In experiments, dimmable LED drivers rated at 20 W exhibited an error of less than 2% when operating from 5 to 20 W and an error of less than 5% when operating from 2 to 5 W.