Mount Everest, the highest peak on Earth, has captivated human imagination for centuries. Accurately determining its height, given its remote location and immense scale, represents a remarkable achievement in scientific history. Early measurements of the mountain, known locally as Chomolungma in Tibet and Sagarmatha in Nepal, were carried out before modern satellite technology. This required surveyors to devise ingenious methods to calculate the altitude of a summit they could not approach, relying on geometry and careful observation.
Laying the Foundation The Great Trigonometrical Survey
The initial effort to map the Indian subcontinent and measure the Himalayas began with the Great Trigonometrical Survey (GTS) in 1802. Launched by the British East India Company, this massive undertaking aimed to accurately map the vast territory, starting from a baseline in southern India. The project was led for a time by Sir George Everest, who served as Surveyor General of India from 1830 to 1843.
The survey’s primary goal was to measure a north-south arc of meridian stretching over 2,400 kilometers, known as the Great Arc. Everest’s team used sophisticated instruments and rigorous methods to establish a precise geographical framework across the entire landmass. The project continued for decades, eventually reaching the foothills of the Himalayas.
George Everest never saw the peak that would later be named after him. Because the independent kingdom of Nepal was closed to foreigners, survey teams were forced to work from observation stations in India, sometimes over 100 miles away. This restriction meant the measurement had to be taken from a distance, adding complexity to the mathematical challenge.
Measuring the Immeasurable Trigonometry and Triangulation
The process used to determine the peak’s height relied on triangulation, a geometric technique. This method establishes a network of interconnected triangles across the landscape, anchored to a single, precisely measured baseline. Surveyors measure the angles inside a triangle from two known points to a third, distant point. They then use trigonometry to calculate the lengths of the unknown sides and the elevation of the distant point.
For the Himalayan peaks, surveyors used massive, specialized instruments called theodolites to measure the horizontal and vertical angles to the summit. These instruments were large and heavy, requiring large teams for transport and operation. By observing the mountain, then known as Peak XV, from multiple stations along the Great Arc, they collected angular data.
This raw data was passed to a team of mathematicians, or “computers,” for the final calculations. The chief computer, Radhanath Sikdar, was the first to determine that Peak XV was the highest mountain in the world in 1852. The calculations had to account for atmospheric refraction and the curvature of the Earth over the vast distances. Sikdar’s meticulous work yielded an initial height of 29,002 feet, which was remarkably close to modern figures.
The Modern Era GPS and Satellite Technology
Today, measuring the height of Everest relies on Global Navigation Satellite Systems (GNSS), which includes the Global Positioning System (GPS). Modern expeditions place a high-precision GPS receiver directly on the summit, recording data from multiple satellites for an extended period. This approach provides a geodetic height relative to a mathematically defined ellipsoid, a smooth model of the Earth’s surface.
To convert this geodetic height into the familiar height above mean sea level, surveyors utilize a detailed model of the geoid. The geoid represents the true, undulating sea level extended under the continents. This process involves extensive gravity measurements taken at various points on the mountain’s slopes using instruments like gravimeters. Since the summit is capped by ice and snow, teams also use ground-penetrating radar (GPR) to distinguish between the snow cap and the actual bedrock height.
The most recent official height was jointly announced by Nepal and China in 2020. They used a combination of GNSS, traditional leveling, and gravity data. The new figure of 8,848.86 meters (29,031.7 feet) reflects the mountain’s constant change due to the ongoing collision of the Indian and Eurasian tectonic plates. This geological activity causes the mountain to slowly rise, necessitating periodic re-measurements.