1. A method for monitoring a welding operation within a welding power supply, comprising: sampling pairs of instantaneous voltage and current values from a welding waveform during a first time period; determining instantaneous energy values from the sampled pairs of instantaneous voltage and current values; summing the instantaneous energy values to determine a total energy input into a weld during the first time period; comparing the determined total energy to an acceptable range of total energy values for the welding operation; determining a length of the weld made during the first time period; and determining an energy input per unit length during the first time period using the determined total energy input and the determined length of the weld.