I've taken the standard NATO OB to develop a lot of my own organizational TOE, at least on the army side. I start at Company and work as high as Army (haven't gotten far enough in game to get to that point yet...), but I've tweaked the sizes so a Division comes out to a size of about 5000, Battalion about 5 times that, Regiment 5 times that, and so on. This also lines up roughly with what I see for my ranks (I'm using US ranks, yes), and at a glance generally lines up with the Ground Combat Command sizes in the game. (I typically see Majors averaging 5k, Lt. Colonels about 15-25k, Colonels tend to be over 100k, etc.)
In some cases, I will have smaller elements (Space Marines, for example), and label them accordingly. But these are more specialized units. Here's my general breakout:
Company -> Major -> 5k max
Battalion -> Lt. Col -> 25k
Regiment -> Col. -> 125k
Brigade -> Brig. Gen. ->625k
Division -> Major Gen. -> 3 mil
Corps -> Lt. Gen -> 15 mil
Army -> General -> 75 mil
For naval, I'm starting to try to break ships out by size - on the warship end. Since a fighter shouldn't be more than 300-400 tons (I think it is), then I look at them like this:
500 - 5000 tons - Corvette
5000 - 15000 - Destroyer
15000 - 25000 - Light Cruiser
25000 - 35000 - Cruiser
35000 - 50000 - Heavy Cruiser
50000 - 75000 - Battleship
75000+ - Dreadnought
Light Carriers would be between 25k and 50k, Regular carriers between 50k and 75k, and Fleet carriers > 75k.
I've not gotten over about 30k yet, so most of this is untested hypothesis... I get a game started and then a patch comes out!