ORIGINAL: dude
It can also be hard for the Union generals depending if you are going by when they received their ranks in the “volunteers” vs. the “regular” army.
Sherman is a good example:
[font="times new roman"]Brig Gen (volunteers) Aug 3, 1861[/font]
[font="times new roman"]Maj Gen (volunteers) May 1st 1862[/font]
Brig Gen (regular army) July 1st 1863 (yes Brig Gen... not a mistake.)
... and consider that in July 1863 he was commanding more than just a brigade.
Rank is irrelevant. In the union army a brigadier general could command anything from a brigade to an army. You have to go by what a general commanded. The union army had both regular army and volunteeer army ranks. They also had brevet(honorary) ranks for both. A union officer could be a regular army captain, a brevet regular army major, a colonel of volunteers, and a brevet brigadier general of volunteers all at the same time. After the war generals reverted to their regular army rank if they stayed in. Custer was a major general of Volunteers in april 1865 but only a regular army 1st lt. When the war ended he was "promoted" from Major General to captain.