'Cubits' in the Bible

(For only Og king of Bashan was left of the remnant of the [the giants known as the] Rephaim. Behold, his bed frame was a bed frame of iron; is it not in Rabbah of the Ammonites? It was nine cubits (12 ft.) long and four cubits (6 ft.) wide, using the cubit of a man [the forearm to the end of the middle finger].)