how many senators votes are required to pass a bill?

50% + 1 of the quorum. Since minimum quorum in the Senate is 51 Senators, the bare minumum it takes to pass a bill through the Senate is 26. If all Senators are present, it takes 51 Senators to pass a bill (assuming all Senators vote). and if there is a 50/50 tie, the Vice President, (President of the Senate) gets to cast the tie-breaker.

51 to pass a bill, but 60 to invoke cloture to end debate.