Radhanath Sikdar (1813-1870) was an Indian mathematician who calculated the height of Peak XV and discovered it to be the tallest mountain above sea level. Peak XV was later renamed as Mount Everest.

Sikdar worked for the Surveyor General of India, a division of the British Raj in India at that time. He joined the Great Trigonometric Survey in 1840 and was educated at the Hindu College (now called Presidency College) in Calcutta, India. In 1854, he started the journal Masik Patrika, for the education and empowerment of Bengali women.

Some Indians, including the former Prime Minister Atal Bihari Vajpayee, are of the opinion that Mount Everest should be named after Sikdar. The peak was re-named as Everest although it already had native names in Nepal, the Himalayan kingdom and erstwhile Tibet (Sagarmatha and Choumoloungma respectively.)

The Department of Posts, India, launched a postal stamp on June 27, 2004, commemorating the establishment of the Great Trigonometric Survey in Chennai, India on April 10, 1802. The stamps feature Radhanath Sikdar and Nain Singh, two significant contributors to society. The Great Arc refers to the systematic exploration and recording of the entire topography of the Indian subcontinent which was spear-headed by the Great Trigonometric Society . It is considered to be one of the largest and most difficult of all human endeavours to date.