how many inches of sand should be in a bunker?

Answer 1

According to the USGA's "How to Conduct a Competition," the settled depth of sand in bunkers should be 4 to 6 inches, except that the faces of bunkers must be shallow enough and firm enough to prevent balls from plugging.

Answer 2

enough for you to hit it out and not bottom out on anything other than sand. i'd say at the absolute least 4 inches.