What Is the Tallest Mountain in the World?

How high is Mount Everest above sea level?

The summit of Mount Everest stands 8,848.86 metres (about 29,032 feet) above sea level.^[3] China and Nepal announced that figure jointly on 8 December 2020; CNN reported that the two countries had finally agreed after more than a decade of dispute over the mountain's height.^[3] Everest sits on Nepal's border with Tibet in the Himalayas, and it is called Sagarmatha in Nepal and Qomolangma in Tibet.^[3]

The official figure includes the snow and ice that cover the summit.^[4] It is 86 cm higher than the height Nepal recognised before, and more than four metres above China's previous official figure, which measured the rock beneath the snow.^[4]

Elevations are normally measured from global mean sea level, the average level of the ocean surface, and by that measure Everest's summit is the highest point on Earth.^[1]

Why did Everest's official height change in 2020?

Everest has been measured many times, with different results.^[4] British colonial surveyors, using trigonometry from the plains of India, first put its height at 8,840 metres in 1856.^[4] An Indian survey later set it at 8,848 metres; CNN dates that survey to 1955, and Nepal was still using the figure in 2005.^[3][4] In 1999 the US National Geographic Society calculated 8,850 metres, a number Nepal never officially recognised.^[4]

China published its own results: 8,848.13 metres in 1975 and 8,844.43 metres in 2005.^[5] The 2005 figure led to a row with Nepal that was settled only in 2010, when the two countries agreed that their numbers referred to different things, one to the height of Everest's rock and the other to the height of its snowcap.^[4]

In 2015 a magnitude 7.8 earthquake struck Nepal, and several scientific studies suggested that the mountain's elevation might have changed.^[3] Nepal began its own re-measurement two years later, and China joined after President Xi Jinping visited Nepal in October 2019.^[3][4] A Nepali survey team carried a satellite receiver to the summit on 22 May 2019, and an eight-member Chinese team reached the top on 27 May 2020.^[6][5] A Chinese surveying expert told the state broadcaster CCTV that the final figure was an average of the Nepali and Chinese measurements.^[4]

How do surveyors measure the height of a mountain?

Heights are measured from the geoid, a model of global mean sea level.^[8] If tides and currents were removed, the ocean would settle into a smoothly undulating surface that rises where gravity is stronger and sinks where it is weaker, and that surface defines zero elevation.^[8] Surveyors extend this imaginary surface beneath the continents using gravity readings on land and complex mathematics.^[8]

Satellite positioning gives a different kind of height.^[7] GPS heights are measured above an ellipsoid, a simple mathematical model of Earth's shape, and they do not match heights above mean sea level.^[7] The gap between the two surfaces, called the geoid height, ranges globally from about +75 to -100 metres, so a satellite height has to be converted with a geoid model.^[7]

The surveys behind the 2020 figure combined levelling, gravity measurements and satellite positioning.^[3] Nepal ran a precise levelling survey over 248 km, from Maadar in Siraha, a district bordering India, to Solukhumbu District, and tied it to sea-level data from the Bay of Bengal that India collected.^[6] Its surveyors used gravity, GNSS (Global Navigation Satellite System) and levelling data to build a geoid model around Everest, then combined it with the satellite data from the summit to fix the height.^[6] The Chinese team installed a GNSS antenna on the summit, measured the depth of the snow and made gravity measurements there, while other surveyors observed from six points below the peak.^[5]

Is Mauna Kea taller than Mount Everest?

Measured from base to summit, it is.^[1][2] Mauna Kea, a volcano on the Big Island of Hawaii, rises 4,205 metres above sea level, but its slopes continue about 6,000 metres below the surface to the deep ocean floor.^[1][2] The U.S. Geological Survey (USGS) gives its total height as nearly 10,211 metres (33,500 feet), considerably more than Everest's height above sea level.^[2] NOAA's National Ocean Service says Mauna Kea rises more than 10,210 metres from base to peak and calls it the tallest mountain on Earth.^[1]

Where the base is placed also matters.^[2] The USGS says Hawaii's Mauna Loa rises more than 4 km above sea level, its underwater slopes reach another 5 km down to the sea floor, and its great mass has pressed that floor down a further 8 km, putting its summit about 17 km above its base.^[2] Mauna Kea's 10,211-metre figure stops at the ocean floor, so the two numbers are not directly comparable.^[2]

Which mountain top is farthest from Earth's centre?

Earth is not a perfect sphere; its constant rotation makes it a little thicker at the equator.^[1] Mount Chimborazo in Ecuador stands just one degree south of the equator, where this bulge is greatest.^[1] Its summit is 6,268 metres above sea level, far lower than Everest's, yet it is more than 2,072 metres farther from the centre of the Earth than Everest's peak.^[1] NOAA therefore calls Chimborazo's summit the highest point above Earth's centre and the closest point on Earth to the stars.^[1]

How do the "tallest mountain" figures compare?

NOAA calls the question of the highest mountain on Earth "debatable".^[1] The three figures below measure different things, so they cannot be ranked on a single scale.

NOAA's page still gives Everest's height as 8,848 metres, the figure in use before the 2020 announcement.^[1][3]