A device for performing a Fast Fourier Transform (FFT) on an input dataset includes an FFT pipeline having a first stage configured to receive the input dataset, a plurality of intermediate stages and a final stage, each stage having a stage input; a computational element; and a stage output; a controller configured to select a size for the FFT; and a multiplexer configured to: receive data output from one of the intermediate stages and data output from the final stage; select one of the received outputs in dependence on the selected FFT size; and output said selection as a result of the FFT on the input dataset.