US Sleeping cars were described based upon their layout. A 12-1 sleeper was 12 "sections" and 1 Drawing Room. A "section" was part of the old pullman layout of an upper and lower berth, partitioned off from the aisle with curtains. Such a car would have 6 sections on each side, and then the aisle would zig-zag around the drawing room, which would be on one side of the car, with a corridor on the other side of it.
A 6-6-4 sleeper had 6 "compartments" (larger than a bedroom), 6 roomettes (small rooms on each side of a center aisle) and 4 double-bedrooms.
A 4-4-2 sleeper had 4 double-bedrooms, 4 compartments, and 2 drawing rooms.
A 10-6 sleeper had 6 bedrooms and 10 roomettes.
A 12-4 sleeper had 4 double-bedrooms and 12 duplexes (duplexes were tiny bedrooms stacked top and bottom, but offset to save space. Funky looking, but cheap, as you could get a lot of people in a little space. Forerunner of the "slumbercoach")
18 and 21 roomettes were also popular, as well as 13 bedroom cars, and 11 double-bedrooms. Other variations existed (such as 10-5 sleepers, which were the same as a 10-6, but with only 5 bedrooms), a 12-5, and a 214, which had 2 drawing rooms and 14 roomettes.
Then, of course, there were other cars which combined both sleeping compartments with lounges or observation sections.
