This is my page of Rebel Regiments. This is from a page on wookiepedia I stumbled on. Thanks Horry from the Pirates Fourm for showing me how to use LDD for visuals.
In a Rebel Squadron, as shown below, there are 9 troopers, a Sergeant, and the Corporal, who can fill the place of an absent(dead, vacationing, sick) Sergeant.
A Rebel Platoon(4 Squads: 36 troopers, 4 sergeants, 4 corporals) is led by a Lieutenant.
A Rebel Company(4 Platoons:16 Squads: 144 troopers, 16 sergeants, 16 corporals, 4 Lieutenants) is led by a Captain.
Sorry for blurriness, I resized pics to fit the uploader, before I learned deeplinking.
There is more to this page at http://starwars.wikia.com/wiki/Alliance_Army in the Command Structure section. Thanks for reading, please comment and explain to me what I can to do become better!