In most cases in most states, criminal verdicts must be unanimous. In other words, each and every member of a given jury must agree in order to acquit or convict the defendant. But there actually isn’t a universal right to a unanimous verdict. The Supreme Court has upheld state laws that require less than complete agreement for conviction—for example, a 10-2 vote in favor of guilt. On the other hand, a 5-1 vote isn’t enough for a verdict when the jury consists of only six members and the offense isn’t petty—verdicts of such juries must be unanimous. (Burch v. Louisiana, 441 U.S. 130 (1979).)
For more information on the jury system, see The Right to Trial by Jury.