BJCP 12A
A fairly substantial English dark ale with restrained roasty characteristics.
Differs from a robust porter in that it usually has softer, sweeter and more caramelly flavors, lower gravities, and usually less alcohol. More substance and roast than a brown ale. Higher in gravity than a dark mild. Some versions are fermented with lager yeast. Balance tends toward malt more than hops. Usually has an "English" character. Historical versions with Brettanomyces, sourness, or smokiness should be entered in the Specialty Beer category (23).
Fuller's London Porter, Samuel Smith Taddy Porter, Burton Bridge Burton Porter, RCH Old Slug Porter, Nethergate Old Growler Porter, Hambleton Nightmare Porter, Harvey's Tom Paine Original Old Porter, Salopian Entire Butt English Porter, St. Peters Old-Style Porter, Shepherd Neame Original Porter, Flag Porter, Wasatch Polygamy Porter
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 The 2008 style guide is obsolete but there is a similar 2015 style that you can view below...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: 1.040-1.052
FG: 1.008-1.014
IBU: 18-35
SRM: 20.0-30.0
ABV: 4.0-5.4%