How many US Supreme Court justices must be present to decide a case?
The Supreme Court requires a quorum of two-thirds of the Court, or at least six justices, to hear a case or conduct a vote. The Chief Justice does not have to be one of the six; in his or her absence, the most senior associate justice is in charge.
Decision require a simple majority, which means five votes if eight or all nine Justices are participating; four votes if six or seven Justices are participating. The general rule is that there must be a number equal to the majority of the members sitting less one. So if there are seven members, at least 3 would have to vote to hear the cases. The majority of 4 less 1 equals 3.