If you don't have a U.S. dollar bill and want a piece of paper with the same dimensions... use any paper and fold in half diagonally from any corner (that's a 45o degree fold, the big arrow) then fold one of the edges to meet the fold you just made (that's 22.5o degrees, small arrow). Then you can cut an horizontal and vertical from any point along that 22.5 to be used as the opposite corner of the bill.