When describing sleepers, what does "4-4-2" or "10-6" or other numbers in that format mean? I'm pretty sure it describes the types/amounts of rooms but that's about all I can figure out...

You are correct, this describes the accommodations the car has.

A 10-6 is a 10 roomette, 6 double bedroom car. That floorplan was manufactured by Budd, Pullman and ACF for various roads (UP Pacific, ATSF Pine and Palm, SP, CB&Q). Some were center bedroom cars as well, with 5 roomettes on either end.

Another plan that comes to mind is 6-6-4 which equates into a 6 roomette, 4 double bedroom, 6 section car (L&N, C&EI and NC&St. L)

There are tons of variations.

MRLX1020

Some others:

lightweight cars
4-4-2 ..... 4 Double Bedroom-4 Compartment-2 Drawing Room
5-2-2 ..... 5 Double Bedroom-2 Compartment-2 Drawing Room
16-4 ...... 16 Duplex Roomette-4 Double Bedroom
8-4-4 ..... 8 Duplex Roomette-4 Double Bedroom-4 Section
8-6-3-1 .. 8 Duplex Roomette-6 Roomette-3 Double Bedroom-1 Compartment
7-4-3-1 .. 7 Duplex Roomette-4 Section-3 Double Bedroom-1 Compartment
14-4 ...... 14 Roomette-4 Double Bedroom
14-2-1 ... 14 Roomette-2 Double Bedroom-1 Drawing Room
6-5-2 ..... 6 Roomette-5 Double Bedroom-2 Compartment

heavyweight cars
12-1 .... 12 Section-1 Drawing Room
10-1-1 .. 10 Section-1 Compartment-1 Drawing Room
10-2-1 .. 10 Section-2 Compartment-1 Drawing Room
10-2 ...... 10 Section - 2 Drawing Room
8-2-1 .... 8 Section-2 Compartment-1 Drawing Room
6-3 ....... 6 Compartment-3 Drawing Room
7-2 ....... 7 Compartment-2 Drawing Room

And he didn't even get into the various observation, lounge, buffet, or parlor car varieties...

Early "10-6 is a 10 roomette, 6 double bedroom car" were "10-5 is a 10 roomette, 5 double bedroom" cars.

Cars with all the same rooms were not usually abbreviated so much:
11 Double Bedrooms
22 Roomettes
24 Duplex Roomettes
6 Double Bedrooms, Lounge
I forget what a solid Drawing Room car was.
Some of the all room cars also had a porters compartment. Some Amtrak and VIA Rail Canada cars had 1 Roomette replaced with a shower. In these cases, the abbreviation may not have been changed.

Long ago, the length of many passenger cars was standardized at about 85 feet, which made it easier to have standard configurations.

One more lightweight:

4-4-5-1 4 roomettes, 4 open sections, 5 double bed rooms, 1 compartment.

I have one, built by PS in 1954. Last sleeper built for FEC. Want to buy it?

-Jim Herron

That would be great, if I had the moneyto buy it.

Oh wow, lots of different combinations then. Thanks!