The island of Nantucket is 14 miles (20 Km) long and 3 - 5 miles (2-3 Km) wide.   On average, total land is 47.8 square miles (123.8 Km). Nantucket has a year-round population of 10,000, but at the peak of the summer, the quaint island flourishes with as many as 56,000 people.