How many justices sit on the U.S. Supreme Court?

How to get close to this number

Judicial panels are small and odd-numbered, for the obvious reason: a court that decides by majority cannot afford ties. That narrows the possibilities immediately to five, seven, nine or eleven, and constitutional supreme courts cluster at the upper end of that range because they need enough members to represent a range of judicial thought.

The fact in the explanation is the one most people do not know: the number is not in the Constitution. It is set by ordinary legislation and has been changed several times, ranging from five to ten, and it has only been stable since 1869. A figure that feels constitutionally fixed is a statutory choice that could be changed by a simple act of Congress.

That distinction between constitutional and statutory is why proposals to change the size resurface periodically and are legally straightforward even when they are politically explosive. When a number feels immovable, it is worth checking whether it is actually entrenched or merely long-standing — the two feel identical and behave completely differently.