This color difference calculator will take input of two sets of LAB color values and calculate the numerical difference expressed as Delta E.
It supports the major calculation methods, CIE 1971, CIE 1994 for both Graphic Arts and Textiles, CIE 2000, and CMC l:c for both imperceptibility and acceptability.
LAB values are typically provided by a spectrophotometer or other known LAB values such as existing color swatches.
Also handy for determining the method your own colorimeters use in Delta calculations.