A system and method for determining rotor speed of an AC induction machine is disclosed. The system is programmed to estimate a rotor speed of the induction machine according to a linear speed estimation algorithm and based on name plate information (NPI) of the induction machine and parameters of the AC induction machine during operation thereof. The rotor speed estimation system is also programmed to estimate a rotor speed of the AC induction machine according to a frequency-domain signal processing algorithm and determine if the rotor speed estimated thereby is valid. If the rotor speed estimated by the frequency-domain signal processing algorithm is valid, then a tuned rotor speed of the AC induction machine is estimated according to the linear speed estimation algorithm and based, in part, on the rotor speed estimated by the frequency-domain signal processing algorithm.