When was the first scientific measurement of the height of Mount Everest made?

During the Great Trigonometrical Survey of India, surveyors in the mid-19th century determined that Mount Everest was the highest mountain then measured in the world. The peak was initially known as Peak XV before being named after Sir George Everest. The first published height estimate appeared in 1856, giving a value close to the mountain’s modern measured height. Everest’s official elevation has since been refined with better instruments and satellite methods. This survey work was a major achievement in geography and geodesy.