Measurement
Radhanath Sikdar, an Indian mathematician and surveyor from Bengal, was the first to identify Everest as the world's highest peak in 1852, using trigonometric calculations based on measurements made with theodolites from 240 km (150 miles) away in India. Before it was surveyed and named, it was known as Peak XV to the survey team.
The
mountain is approximately 8,850 m (29,035 feet) high, although there
is some variation in the measurements. The 1998 American Everest Expedition
installed a GPS unit on the highest bedrock, computing the elevation of the
summit as 8,830 meters. Neither the government of Nepal nor the PRC have
officially recognised this measurement, and still consider the official height
of Everest to be 8,848 m.
It was first measured in 1856 at 29,000 feet (8,839 m), but declared to be 29,002 feet (8,840 m) high. The arbitrary addition of 2 feet (0.6 m) was to avoid the impression that an exact height of 29,000 feet was nothing more than a rounded estimate.
In the 1950s an Indian survey made closer to the mountain also using theodolites gave another often quoted figure of 8,848 m (29,028 feet). Today's generally accepted value of 8,850 m (29,035 feet) was obtained via GPS readings from a device placed on the summit by the USA in 1999. Everest is still growing due to the plate tectonics of the area, adding 3 to 5 mm to the height and moving north-eastward at 27 mm per year.
Everest is the mountain whose summit attains the greatest distance above sea level. Two other mountains are sometimes claimed as alternative "highest mountains on Earth". Mauna Loa in Hawaii is highest when measured from its base; it rises over 9 km when measured from its base on the mid-ocean floor, but only attains 4,170 m above sea level. The summit of Chimborazo in Ecuador is 2,168 m farther from the Earth's centre (6384.4 km) than that of Everest (6382.3 km), because the Earth bulges at the Equator. However, Chimborazo attains a height of 6,310 m above sea level, by which criterion it is not even the highest peak of the Andes.
The deepest spot in the ocean is deeper than Everest is high: the Challenger Deep, located in the Mariana Trench, is so deep that if Everest were to be placed into it, it would have more than 2 km of water covering it.