According to the United States Census Bureau, the town has a total area of , of which is land and is water, comprising 2.31% of the town. The highest points in Bath are a trio of knobs on Gardner Mountain, all found near the northernmost point in town and all measuring slightly greater than above sea level. The Connecticut River forms the western boundary of the town; the Ammonoosuc and Wild Ammonoosuc rivers flow through the town. Bath lies fully within the Connecticut River watershed.