A sub-mm ranging system, which estimates the time of flight of a RF signal between two nodes using Time of Arrival (ToA) estimation, is possible according to maximum likelihood estimator simulations and theoretical bounds on ToA estimation. In this paper we propose a frequency domain based ToA estimator for an indoor ranging system which is broken into 3 computational steps towards an efficiently implementable estimator. Performance of this hardware efficient estimator is comparable with the maximum likelihood estimator's and it is computationally efficient. Complexity of the computational steps can be traded off against each other. Moreover, the implementation-aware estimator provides high flexibility on choosing between transmitted signal energy, computational cost and precision of the ranging algorithm. In this work, a simulation precision better than 1 mm is obtained for SNRs below 0 dB, by transmitting an OFDM (Orthogonal Frequency Division Multiplexing) like signal whose duration is 9 mu s, with a 6 GHz bandwidth on a 60 GHz carrier.