If an official was impeached by the house, how many senators would have to vote for conviction in order for the official to be found guilty?

In the United States it is a two step process. First, the House of Representatives must pass a movement to actually impeach the official in question, which means they deliver a formal statement of legal charges, by a simple majority vote. If that passes, then the Senate must vote to convict, and thereby remove from office, the official by a two-thirds majority vote. To be clear, convicting an official with the Impeachment process does NOT criminally convict them. It only removes them from office and a subsequent, later, vote decides if they can ever hold that, or any, office again. Any actual criminal proceedings are separate and held separately.