Six U.S. Supreme Court justices are needed to form a quorum.
The rule comes from 28 U.S.C. § 1, which provides that the Court consists of one Chief Justice and eight associate justices and that “any six” constitute a quorum. A quorum is the minimum number of members who must be present for the Court to conduct official business; it is not the number needed to win a case.
That distinction matters. A six-member quorum can hear and decide cases, but a tie vote produces no controlling majority and generally leaves the lower court’s judgment in place. The Court normally has nine justices, so six is a statutory minimum rather than its usual operating number.
The wrong options reflect nearby but different ideas. Seven is not the quorum threshold, four is too few under the statute, and five is one short. The number of justices has changed historically, but the modern nine-member structure and six-member quorum are set by federal law, not directly by the Constitution.