Kaua?i or Kauai (pronounced /?ka?.a?/ in English and [kou???i] or [k?u???i] in Hawaiian) is the oldest of the main Hawaiian Islands. With an area of 552.3 square miles (1,430.5 km2), it is the fourth largest of the main islands in the Hawaiian archipelago and the 21st largest island in the United States. Known also as the “Garden Isle”, Kaua?i lies 105 miles (170 kilometers) across the Kaua?i Channel, northwest of O?ahu.