Te lo voy a poner en ingles:
Rangos:
http://www.army.mil/symbols/Downloads/Ranks.pdf
PRIVATE
(Addressed as "Private")
Lowest rank: a trainee who’s starting Basic Combat Training (BCT). Primary role is to carry out orders issued to them to the best of his/her ability. (PVT does not have an insignia)
PRIVATE FIRST CLASS (PFC)
(Addressed as "Private")
PV2s are promoted to this level after one year—or earlier by request of supervisor. Individual can begin BCT at this level with experience or prior military training. Carries out orders issued to them to the best of his/her ability.
SPECIALIST (SPC)
(Addressed as "Specialist")
Can manage other enlisted Soldiers of lower rank. Has served a minimum of two years and attended a specific training class to earn this promotion. People enlisting with a four year college degree can enter BCT as a Specialist.
CORPORAL (CPL)
(Addressed as "Corporal")
The base of the Non-Commissioned Officer (NCO) ranks, CPLs serve as team leader of the smallest Army units. Like SGTs, they are responsible for individual training, personal appearance and cleanliness of Soldiers.
SERGEANT (SGT)
(Addressed as "Sergeant")
Typically commands a squad (9 to 10 Soldiers). Considered to have the greatest impact on Soldiers because SGTs oversee them in their daily tasks. In short, SGTs set an example and the standard for Privates to look up to, and live up to.
STAFF SERGEANT (SSG)
(Addressed as "Sergeant")
Also commands a squad (9 to 10 Soldiers). Often has one or more SGTs under their leadership. Responsible for developing, maintaining and utilizing the full range of his Soldiers' potential.
SERGEANT FIRST CLASS (SFC)
(Addressed as "Sergeant")
Key assistant and advisor to the platoon leader. Generally has 15 to 18 years of Army experience and puts it to use by making quick, accurate decisions in the best interests of the Soldiers and the country.
MASTER SERGEANT (MSG)
(Addressed as "Master Sergeant")
Principal NCO at the battalion level, and often higher. Not charged with all the leadership responsibilities of a 1SG, but expected to dispatch leadership and other duties with the same professionalism.
FIRST SERGEANT (1SG)
(Addressed as "First Sergeant")
Principal NCO and life-blood of the company: the provider, disciplinarian and wise counselor. Instructs other SGTs, advises the Commander and helps train all enlisted Soldiers. Assists Officers at the company level (62 to 190 Soldiers).
SERGEANT MAJOR (SGM)
(Addressed as "Sergeant Major")
SGMs experience and abilities are equal to that of the CSM, but the sphere of influence regarding leadership is generally limited to those directly under his charge. Assists Officers at the battalion level (300 to 1,000 Soldiers).
COMMAND SERGEANT MAJOR (CSM)
(Addressed as " Command Sergeant Major")
Functioning without supervision, a CSM’s counsel is expected to be calm, settled and accurate—with unflagging enthusiasm. Supplies recommendations to the commander and staff, and carries out policies and standards on the performance, training, appearance and conduct of enlisted personnel. Assists Officers at the brigade level (3,000 to 5,000 Soldiers).
SERGEANT MAJOR OF THE ARMY
There’s only one Sergeant Major of the Army. This rank is the epitome of what it means to be a Sergeant and oversees all Non-Commissioned Officers. Serves as the senior enlisted advisor and consultant to the Chief of Staff of the Army (a four-star General).
WARRANT OFFICER 1 (WO1)
(Addressed as "Mister")
Expert in certain military technologies or capabilities (e.g.,- helicopter pilots). Soldiers with this rank serve under a warrant from the Secretary of the Army. WOs are single-track specialty officers, experts and trainers who, by gaining progressive levels of expertise and leadership, operates, maintains, administers and manages the Army's equipment, support activities or technical systems for their entire career.
CHIEF WARRANT OFFICER 2 (CW2)
(Addressed as "Chief")
Has received a commission from the president, thus are direct representatives of the president of the United States. Have the authority of Commissioned Officers (who are generalists), but in contrast WOs are specialists. They command detachments, units, activities and vessels as well as lead, coach, train and counsel subordinates.
CHIEF WARRANT OFFICER 3 (CW3)
(Addressed as "Chief")
As leaders and technical experts, Chief Warrant Officers provide valuable skills, guidance, and expertise to commanders and organizations in their particular field.
CHIEF WARRANT OFFICER 4 (CW4)
(Addressed as "Chief")
Chief Warrant Officers remain single-specialty Officers whose career track is oriented towards progressing within their career field rather than focusing on increased levels of command and staff-duty positions.
CHIEF WARRANT OFFICER 5 (CW5)
(Addressed as "Chief")
The grades (CW2—CW5) reflect salary increases and are normally indicative of the length of time a person has served as a Warrant Officer. The grades do not signify differences in job duties.
SECOND LIEUTENANT (2LT)
(Addressed as "Lieutenant")
Typically the entry-level rank for most Commissioned Officers. Leads platoon-size elements consisting of the platoon SGT and two or more squads (16 to 44 Soldiers).
FIRST LIEUTENANT (1LT)
(Addressed as "Lieutenant")
A seasoned lieutenant with 18 to 24 months service. Leads more specialized weapons platoons and indirect fire computation centers. As a senior Lieutenant, they are often selected to be the Executive Officer of a company-sized unit (110 to 140 personnel).
CAPTAIN (CPT)
(Addressed as "Captain")
Commands and controls company-sized units (62 to 190 Soldiers), together with a principal NCO assistant. Instructs skills at service schools and combat training centers and is often a Staff Officer at the battalion level.
MAJOR (MAJ)
(Addressed as "Major")
Serves as primary Staff Officer for brigade and task force command regarding personnel, logistical and operational missions.
LIEUTENANT COLONEL (LTC)
(Addressed as "Lieutenant Colonel " or "Colonel")
Typically commands battalion-sized units (300 to 1,000 Soldiers), with a CSM as principal NCO assistant. May also be selected for brigade and task force Executive Officer.
COLONEL (COL)
(Addressed as "Colonel")
Typically commands brigade-sized units (3,000 to 5,000 Soldiers), with a CSM as principal NCO assistant. Also found as the chief of divisional-level staff agencies.
BRIGADIER GENERAL (BG)
(Addressed as "General")
Serves as Deputy Commander to the commanding general for Army divisions. Assists in overseeing the staff's planning and coordination of a mission.
MAJOR GENERAL (MG)
(Addressed as "General")
Typically commands division-sized units (10,000 to 15,000 Soldiers).
LIEUTENANT GENERAL (LTG)
(Addressed as "General")
Typically commands corps-sized units (20,000 to 45,000 Soldiers).
GENERAL (GEN)
(Addressed as "General")
The senior level of Commissioned Officer typically has over 30 years of experience and service. Commands all operations that fall within their geographical area. The Chief of Staff of the Army is a four-star General.
GENERAL OF THE ARMY (GOA)
This is only used in time of War where the Commanding Officer must be equal or of higher rank than those commanding armies from other nations. The last officers to hold this rank served during and immediately following WWII.
, en Global Security encontre datos sobre los numeros de las FFAA de Estados Unidos, sumando todo eso da al rededor de 2 millones de reservistas, aqui dejo el link 
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