If there are a total of 535 congressman where does the total of 538 electoral votes come from?

The District of Columbia does not have a voting congressional delegation. However, under the 23rd amendment, the District is entitled to the same number of electoral votes as the state with the least number of electoral votes in presidential elections. Since the states with the least number of votes have three votes, the Washington D.C. is entitled to three electoral votes, so there are 538 total votes even though there are only 535 congresspeople.