Three-phase apparatus such as rectifiers and inverters are widely used in industrial applications. To achieve the required performance, these power converters are controlled using digital signal processors (DSPs) that implement relatively complex embedded control software. Along with the mandatory real-time code that controls the switching of the converter, these DSPs also need to measure, compute, estimate, monitor and report other quantities of interest like active and reactive power, rms value of voltages and currents, magnitude of the fundamentals and of the 5th, 7th, 11th, 13th harmonics, total harmonic distortion (THD), power factor etc. Therefore, along with the primary control code that generates switching signals for the converter, the DSP needs software that computes all these quantities and reports or displays them. This paper considers a three-phase rectifier and presents a method to compute the rms value of the line current, the magnitude of the fundamental, the magnitudes of the 5th, 7th, 11th and 13th harmonics, the THD; also, the harmonic power factor, the displacement power factor and the total power factor. The paper shows the mathematics involved as well as simulations. The method can be applied to other three-phase converters.