Nine justices serve on the U.S. Supreme Court.
The current structure consists of one chief justice and eight associate justices. The Constitution creates “one supreme Court” but does not set a permanent number of members; Congress has changed the Court’s size through legislation. The Judiciary Act of 1789 initially established six justices.
The number changed several times as the nation expanded. Congress set the Court at seven members in 1807, nine in 1837, and ten during the Civil War in 1863. The Judiciary Act of 1869 returned the Court to nine members, where it has remained. Any change to that number would require an act of Congress, not a decision by the justices themselves.
Nine is therefore the standard answer for the Court as currently constituted, but it is not a constitutionally fixed figure. President Franklin D. Roosevelt’s 1937 proposal to add justices became known as the court-packing plan. It failed in Congress, leaving the nine-member arrangement intact.