Malt colour units first
Start by pooling the colour contribution of every grain, weighted by how much of it there is and how concentrated the batch will be.
For a bill with several malts, work out the MCU of each and add them together before converting. The calculator above takes one grain at a time, so for a multi-malt recipe sum the MCU values yourself and enter the total as a single grain at 1 °L per pound-per-gallon.
Why MCU alone is not enough
MCU is linear, and colour is not. Doubling the dark malt does not double the perceived colour — beyond about 10 MCU the relationship flattens hard, because the beer is already absorbing most of the light passing through it. Dennis Morey's power fit corrects for this.
EBC, used through most of Europe, is very close to double SRM.
Rough landmarks
- 2–3 SRM — pale lager, pilsner
- 4–6 SRM — pale ale, blonde
- 8–14 SRM — amber, märzen
- 16–24 SRM — brown ale, dunkel
- 25–35 SRM — porter
- 35+ SRM — stout, effectively opaque
Treat this as a target, not a promise
Colour is the least predictable number on brew day. Boil length and vigour drive Maillard reactions that darken the wort. Mash pH shifts extraction from dark grains. The stated °Lovibond of a malt is a batch average with real spread, and crystal malts vary most. Kettle caramelisation on a direct-fired system adds colour that no grain-bill model can see.
Being two or three SRM off the estimate is completely normal and almost never a problem. Being ten off usually means something about the process, not the arithmetic.