Several different measures have been employed in the literature to describe performance by human observers in intensity discrimination tasks. These measures include the difference limen (DL) or ’’ΔI in dB,’’ the Weber fraction (ΔI/I), and signal-to-masker ratio (Ps/Pm). This article describes the mathematical relationship among these measures for conditions in which masker and signal are (1) sinusoids of the same frequency; (2) sinusoids of different frequencies; and (3) noise waveforms. We provide a table which contains values of each of these measures, describing equivalent performance over the typical range obtained in most intensity discrimination experiments. We express some cautions that should be observed in choosing and reporting particular measures of intensity discrimination.