US Presidential election: 583 Electoral College votes are up for grabs

US voters don't elect their president directly. Instead representatives called electors have the final say on who makes it to the White House. In total, there are 538 of them in the electoral college. The number from each state varies depending on population. It is a system that has at times proved controversial because a candidate doesn't necessarily need the majority of the national vote to secure a majority of electors. That was the case in 2016, when Donald Trump lost the popular vote, but beat Hillary Clinton to the White House.