Reply #101: 60 to keep a bill from being voted on. 50 plus the VP to pass or defeat a bill that does manage to

[No Elephants]

get to a vote somehow.

And 67 to change any Senate rule.

Those are all products of Senate rules, not the Constitution, which simply allows each House to make rules for its own governance.

Senate rules express the numbers in percentages, though, because you can't assume there will always be 50 states and therefore 100 Senators.