How long is a term for a U.S. senator?

Why this is the answer

A U.S. senator is elected for six years. Representatives serve two and the President four, so the Senate term is the longest of the three and three times the House term. The length was a choice. The framers wanted one part of Congress that would not swing with every change in public mood, and the 2008 study lessons explain that they gave senators a fairly long term so they could be independent from public opinion and balance the shorter House terms. The Federalist Papers made the same case. Federalist No. 62 says a body meant to correct sudden and violent passions needs great firmness, and so should hold its authority for a considerable time, and it warns that a rapid succession of new members brings a change of opinions and, after it, a change of measures. The Constitution also staggers Senate terms. When the first Senate met, its members were divided into three classes, so that one third of the seats are chosen every second year. Senate elections take place in even-numbered years, and the chamber is never replaced all at once: after any general election, two thirds of the senators were not on the ballot. There is no limit on how many terms a senator may serve. Running for the Senate has its own requirements. A candidate must be at least 30 years old, a U.S. citizen for at least nine years, and an inhabitant of the state. For the House the figures are 25 years of age and seven years of citizenship. Six years is the answer. The common error is trading it with another office: two years is a House term, four years is the President's, and eight years is the most a President can be elected to serve, across two terms. Counting up by twos from the House to the President to the Senate keeps them in order.