How many federal supreme Court justices are there?

There are nine

Explanation:

Nine Justices make up the current Supreme Court: one Chief Justice and eight Associate Justices. The Honorable John G. Roberts, Jr., is the 17th Chief Justice of the United States, and there have been 102 Associate Justices in the Court's history.

The answer is

Nine Justices make up the current Supreme Court: one Chief Justice and eight Associate Justices. The Honorable John G. Roberts, Jr., is the 17th Chief Justice of the United States, and there have been 102 Associate Justices in the Court's history.