Which percentage of senators is needed to convict an individual at an impeachment trial?

Well actually nobody can be guilty of impeachment, because impeachment isn't a crime. Impeachment is the process by which Congress charges a federal official with a crime and the subsequent trials associated with the criminal act. Most commonly federal officials are impeached on charges of treason or misconduct in their role as a government official. In order for someone to be impeached and removed from office 2/3 of Congress must vote in favor of his or her removal.