The United States House of Representatives has 435 voting members. Those representatives serve two-year terms and are distributed among the states according to population, with every state guaranteed at least one seat.
Congress did not always have a fixed size. As the country’s population grew, the number of representatives regularly increased. The Apportionment Act of 1911 set the voting membership at 435, and the Reapportionment Act of 1929 established the cap that remains in effect. The temporary admission of Alaska and Hawaii raised the number to 437 from 1959 to 1963, after which it returned to 435.
The House also includes six non-voting members representing the District of Columbia and certain U.S. territories, so “435” specifically means voting representatives. That distinction explains why the answer is different from 538, the total number of presidential electors, and 100, the number of U.S. senators. Each House member represents one congressional district.