Steam quality is the proportion of saturated steam (vapor) in a saturated condensate (liquid)/steam (vapor) mixture. A steam quality of 0 indicates 100 percent liquid (condensate), while a steam quality of 100 indicates 100 percent steam. One pound of steam with 95 percent steam and 5 percent of liquid entrainment has a steam quality of 0.95.

The measurements needed to obtain a steam quality measurement are temperature, pressure, and entrained liquid content. A high percentage (88 percent or more) of industrial steam systems use saturated steam for process applications. Saturated steam (meaning steam that is saturated with energy) is completely gaseous and contains no liquid.