As electronic industries grow more and more, there are many applications with motors. In a car system, there are also many parts adopting motors. These motor systems can be controlled with their frequency information obtained from motor currents, hall sensor output, tachometer and etc. In this paper, we use a WRLS(Weighted Robust Least Square) estimator  to estimate motor frequency with the signal gets from a linear hall sensor. To prove its performance, we compare the estimates from WRLS estimator with those from an analog tachometer. Experimental results show that the WRLS estimator works well in varying frequency and sensor bias situation. However, the WRLS estimator has defects at low frequency or over the discontinuous bias variation of a linear hall sensor.