59 square kilometers

Photo from Wikimedia Commons
Manhattan Island
The 59-square-kilometer island at the center of New York City/Islands
Manhattan is a narrow island at the confluence of the Hudson and East Rivers, serving as the economic and cultural heart of New York City. Measuring just 21.6 km long and 3.7 km at its widest, its 59 square kilometers contain Wall Street, Times Square, Central Park, and the densest urban core in the United States. About 1.6 million people live on the island, with the daytime population swelling to nearly 4 million as commuters arrive. The island was famously purchased from the Lenape people in 1626.
Measurements
North to south
At 14th Street area
Approximate shoreline
Bennett Park in Washington Heights
Typical north-south block