In this paper, a method for online estimation of the tip speed ratio (TSR) of small wind turbines is presented, in order to evaluate the MPPT performance. Unlike obvious methods, for which an encoder or resolver is needed, the presented method only requires measurements of the wind speed and the generator current. Firstly, the accuracy of the presented method is evaluated by using a wind turbine emulator. The obtained results show that the method is suitable for accurately determining both the shaft speed and the TSR of a small wind turbine. This method of estimating the TSR is promising given its simplicity and applicability in the full range of synchronous generators. In addition, by comparing the estimated TSR with the optimum TSR, the MPPT performance can be evaluated. Secondly, the TSR of a commercially available small wind turbine is measured by using the presented method and the MPPT performance is evaluated. In conclusion, the MPPT of the tested turbine can be improved, allowing a considerable increase in the yearly energy output.