SRM (Standard Reference Method)
The SRM is a unit that measures the color of a beer.
The lower the number, the lighter the beer; the higher it is, the darker it is.

• SRM 2 to 5: very pale blond (light beers, pilsner, lager)

• SRM 6 to 15: golden to amber (ales, IPA, amber)

• SRM 16 to 30: copper to brown (brown ale, bock)

• SRM 30 and above: very dark to black (porter, stout)

This measurement comes from a test of light transmission through the beer, standardized to obtain a scale common to all brewers.