One and a half spins (540°), FS or BS. You need to manage rotation speed and landing timing, with the handle passed, wrapped, or in a baller style depending on your style.
Tips to land it
Only attempt the 540 once you have mastered the 360 on both sides (FS and BS).
Take more entry speed than for a 360 to have time to finish the rotation and a half.
Let your gaze follow your body, only look for the water at the end of the rotation.
Anticipate the landing slightly: open up a bit before the end of the turn to avoid over-rotating.