In federal criminal cases, the number of jurors must be 12. Federal Rule of Criminal Procedure Rule 23 provides: “A jury consists of 12 persons unless this rule provides otherwise.” This is in contrast to federal civil cases, where there often are only six jurors. State criminal cases range from between 6 to 12 jurors.

Can a state conduct a criminal trial with only five jurors?

No, the United States Supreme Court ruled in Ballew v. Georgia (1978; see LegalSpeak, p. 168) that a state could not conduct a criminal trial with less than six jurors, because a five-member jury would violate a criminal defendant’s right to a jury trial guaranteed by the Sixth Amendment. The court cited empirical research showing a correlation between jury size and good results. “As juries decrease in size, then, they are less likely to have members who remember each of the important pieces of evidence or argument,” Justice Harry Blackmun wrote the Court.