Sea level is the height of the ocean’s surface at a certain spot and depends on changing conditions. It is also the basis for most Earth surface measurements, because sea levels are used as a reference point in determining land elevations and ocean depths.

Scientists have averaged out the highest and lowest altitudes and depths from sea level locations: The highest is Mount Everest (Nepal-Tibet), which has been measured at 29,022 feet, 7 inches (8,846 meters) above sea level, although China and Nepal have their own numbers, both agreeing on 29,029 feet (8,848 meters) above sea level. (The differences are because no one knows where to measure the height from—the ground or snow height; it may eventually be a moot point, since the ice melts and the ground is rising as the Indian continent is being pushed beneath China and Nepal.) The lowest point on land is the Dead Sea (Israel-Jordan), which measures 1,299 feet (396 meters) below sea level. The greatest depth below sea level is the Mariana Trench in the Pacific Ocean—a deep chasm measuring 36,201 feet (11,033 meters) below sea level.