[Heartofsong83]

What happens if some Senators don't vote and the vote is, say, 59-38? That is over 60%...

[Cboldt]

What happens if some Senators don't vote and the vote is, say, 59-38? That is over 60%

Three-fifths of Senators duly chosen and sworn, so it is a certain number of votes. AS the Senate now has 100 members, duly selected and sworn, exactly 60 votes are needed to pass a cloture motion.

http://rules.senate.gov/senaterules/rule22.php