A platoon in the United States Army typically contains 16-40 soldiers. A platoon is the second smallest grouping of soldiers; and, it is usually lead by a lieutenant.
The U.S. Army is organized in small groups, joined together to form larger groups; and, each group is lead by an officer. High-ranking officers lead larger groups of soldiers.
The smallest group is a squad comprised of 4-10 soldiers and lead by a staff sergeant. Other well known groups include battalions of 500 to 600 soldiers lead by a lieutenant colonel and a brigade of 3,000 to 5,000 soldiers lead by a colonel. A field army lead by a general is the largest group consisting of at least 40,000 soldiers.