According to the United States Census Bureau, the town has a total area of , of which is land and (0.89%) is water. The highest point in Chatham is the summit of South Baldface, with an elevation of above sea level. Sable Mountain, elevation , is in the west, and Robbins Ridge crosses the center of Chatham from east to west. Upper Kimball Pond is in the southeast, and Basin Pond in the northeast. Chatham lies fully within the Saco River watershed.