A two-thirds majority vote in both the House of Representatives and in the Senate is required to override a presidential veto. The exact number depends on how many representatives vote; therefore, the actual number is subject to change.
If all 435 members of the House of Representatives votes, then at least 290 must vote to override. If all 100 Senate members vote, then at least 67 must vote for the veto. A two-thirds vote is technically considered a supermajority, which is much more difficult to get than a traditional simple majority. Fewer than 10 percent of all presidential vetoes have been overridden by a vote in the chambers of Congress.