Colorimetric determinations of dye contents on polyester fibers evolved as a viable alternative to many hours of determining dye contents on fibers by soxlet extractions. Experimental work indicates a simple linear relationship between the amount of dye on the fabric and the color “appearance” of the fabric (as measured by a colorimeter). Varying dyeing procedures and dye carriers showed negligible effects on the correlation. Therefore, varying the penetration and fixation of the dye in the fiber were unimportant factors in this type of measurement. The established calibrations only relate to systems using identical fabric-dye combinations since both the dye and the fiber will affect colorimetric readings. The technique is applicable to any combination of fabric and dye (except pile fabrics), given the appropriate calibration. Where repeated determinations of dye contents on large quantities of similarly dyed fabrics will be required, colorimetric dye content determinations will save time and money.