To convict a president in a U.S. Senate impeachment trial, you need a two‑thirds majority of senators who are present for the vote , not just a simple majority.

In practical terms:

  • If all 100 senators are present, conviction requires 67 guilty votes.
  • If fewer than 100 are present, it’s still two‑thirds of those present (for example, if 90 were present, you’d need 60 votes to convict).

So the short, direct answer to “how many votes do you need to convict a president in the Senate?” is: two‑thirds of the senators present (typically 67 out of 100).