The maximum is 560. This is achieved by placing a Q or Z, with a normal value of 10, on a double letter score on the edge of the board, as part of a 15-letter word (such as BENZOXYCAMPHORS) covering three triple word score squares. This gives a value of 10 × 2 × 3 × 3 × 3 = 540. For the extra 20 points, the Z must also happen to make another, perpendicular word.