A cross correlation fluid flow meter including a body having first and second sensor devices positioned such that in use they are spaced apart a known distance in the direction of fluid flow, each sensor device having a signal transmitter and a signal receiver. According to one embodiment of the flow meter, the signal transmitter of the first sensor device is operable to transmit signals at a first frequency and the signal receiver of the first sensor device is arranged to receive signals at the first frequency. The signal transmitter of the second sensor device is operable to transmit a second signal at a second frequency and the signal receiver of the second device is operable to receive signals at the second frequency, the first and second frequencies being different from one another. The first sensor is non-responsive to the second frequency and the second sensor is non-responsive to the first frequency. Cross correlation of the received signals provides an indication of the fluid flow rate.