"Stout" isn't one SRM number — it's a family covering a genuinely wide range, from a dry Irish stout at the lighter end through a Russian imperial stout at the very darkest end most homebrewing grain bills ever reach.
The range across stout sub-styles
- Dry Irish stout: roughly 25-40 SRM — dark, but at the lower end of what "stout" covers.
- Sweet/milk stout: roughly 30-40 SRM, similarly dark but built around a different malt and sweetness profile.
- Oatmeal stout: roughly 22-40 SRM.
- Foreign extra stout: roughly 30-40 SRM.
- Russian imperial stout: roughly 30-40+ SRM by style guideline, though real-world imperial stout grain bills — loaded with roasted barley and dark specialty malt to support their strength — often compute well past 40.
A real grain bill, computed
A representative imperial stout grain bill — 3.6 kg pale base malt (2°L), 0.45 kg chocolate malt (400°L), and 0.45 kg black patent malt (500°L), in a 19 L batch — computes to roughly 52.8 SRM. Run this exact grain bill to see the swatch, which by this point renders essentially black — the SRM scale keeps climbing numerically well past the point where the human eye can distinguish further darkening, and 52.8 looks indistinguishable from 40 or 90 in a glass even though the numbers themselves keep separating.
Why the numeric range and the visual range diverge at this end
At the pale end of the scale, a few SRM points make an obvious visual difference — the gap between straw and gold is easy to see. At the dark end, the same size gap in SRM points is visually meaningless; a beer computing to 45 SRM and one computing to 90 SRM both simply look black in a glass, even though the formula keeps producing different numbers. This is why competition guidelines for the darkest styles often just specify a range like "30-40+" rather than pretending a precise number matters the way it does for a pale lager.
What actually drives a stout this dark
A small quantity of very dark specialty grain contributes disproportionately more colour than a much larger quantity of pale base malt — see how much roasted barley makes a beer black for exactly how little it takes. If your own stout is computing noticeably lighter than expected, check the actual weight and Lovibond rating of your dark specialty grains against the malt reference before assuming the recipe itself is wrong — a modest change in dark-grain percentage moves SRM more than almost any other single grain-bill decision.