Private, E-1: PVT
Private, E-2: PV2
Private First Class, E-3: PFC
Specialist (Old Spec4): Spec; (SP4)
Sergeant, E-5: SGT
Staff Sergeant, E-6: SSG
Sergeant First Class, E-7: SFC
Master Sergeant, E-8: MSG
First Sergeant, E-8: 1SG
Sergeant Major, E-9: SGM
Command Sergeant Major, E-9: CSM
Second Lieutenant, 0-1: 2LT
First Lieutenant, 0-2: 1LT
Captain, 0-3: CPT
Major, 0-4: MAJ
Lieutenant Colonel, 0-5: LTC
Colonel, 0-6: COL
Brigadier General, 0-7: BG
Major General, 0-8: MG
Lieutenant General, 0-9: LTG
General, 0-10: GEN
Say, isn't it the letter "O" for officer, and not "oh" meaning zero? I say that because enlisted ranks are abbreviated "E."
Those are Army abbreviations. USAF O-5 = Lt Col