How big is Sydney Harbour?

Sydney harbour is 12 miles (19 km) long with a total area of 21 square miles (55 square km) . It has minimum and maximum depths of 30 feet (9 metres) and 155 feet at low water, and its irregular foreshores extend more than 150 miles

http://www.britannica.com/EBchecked/topic/470897/Port-Jackson

Paul :)