BJCP 13B
A very dark, sweet, full-bodied, slightly roasty ale. Often tastes like sweetened espresso.
Gravities are low in England, higher in exported and US products. Variations exist, with the level of residual sweetness, the intensity of the roast character, and the balance between the two being the variables most subject to interpretation.
Mackeson's XXX Stout, Watney's Cream Stout, Farson's Lacto Stout, St. Peter's Cream Stout, Marston's Oyster Stout, Sheaf Stout, Hitachino Nest Sweet Stout (Lacto), Samuel Adams Cream Stout, Left Hand Milk Stout, Widmer Snowplow Milk Stout
You can view the complete style details on the BJCP website. The 2008 style guide is obsolete but there is a similar 2015 style that you can view below...
OG: 1.044-1.060
FG: 1.012-1.024
IBU: 20-40
SRM: 30.0-40.0
ABV: 4.0-6.0%