The Standard Reference Method, abbreviated as SRM is the color system used by brewers to specify finished beer and malt color. In the case of malt it is actually the SRM color of a laboratory wort made from the malt which is printed on the package. The SRM value is 12.7 times the log of the attenuation experienced by light of wavelength 430 nanometers (deep blue) in passing through 1 cm of the beer (or wort). The scaling factor (12.7) and path were chosen (1951) to make SRM values correspond closely to values measured in the Lovibond system which was in use at the time. The two systems are approximately equivalent for home brewing applications. SRM is also sometimes referred to Standard Research Method by some books but this is incorrect. Below are some approximate SRM color ranges.
1.0 - 3.0 SRM - Pale yellow color 3.0 - 4.5 SRM - Medium yellow 4.5 - 7.5 SRM - Gold 7.5 - 9.0 SRM - Amber 9.0 - 11.0 SRM - Copper 11.0 - 14.0 SRM - Red/Brown 14.0 - 19.0 SRM - Brown 20.0 SRM - Black
The European Brewing Convention has specified a nearly identical system for beer color reporting. The only difference between SRM and EBC is that in the EBC system the log attenuation is multiplied by 25 rather than 12.7. Thus EBC color is approximately twice SRM color.