This paper shows how to analyze Total Harmonic Distortion (THD) using the fast Fourier transformation (FFT) capability of low-cost digital sampling oscilloscopes. It was found that THD measurements using this method are accurate within less than a few percent of absolute error. A high level of accuracy can be achieved as long as the measured THD is sufficiently large (> 3.2 %) in order to not subceed the dynamic range of common 8-bit digital storage oscilloscopes. The method presented herein is particularly convenient if only a coarse, relative indicator of THD improvement or degradation is needed.