Bharatiya Jyotihshastra (History of Indian Astronomy), translated by R. V. Vaidya v2.c12.s3.31

v2.c12.s3.31

It cannot be determined with certainty what distance was denoted by ‘yojana’. Hence, there is no reliable means to test the accuracy of these diameters of the earth mentioned in our works. According to the views of most of our works, one Yojana is equal to 32000 cubits, and if one cubit be assumed to be equal to 19.8 inches, the Yojana, in English miles, will be exactly 10 miles. Hence, the diameter of the earth, accepting the lowest figure, that given by the Pañca Siddhāntikā, would be 10186 miles. According to modern astronomy, the diameter of the earth, east to west, is 7925 miles. But the measure of yojana may have been somewhat smaller. The dictionaries known as Vācaspati and Śabdārṇava give 16000 cubits as the length of the yojana, which makes a yojana equal to 5 miles. In the middle of the 7th century A.D. Hjouen Thsang, a Chinese traveller, had visited India. He has described the whole of India. He has given distances of cities and places in terms of the Chinese measure, called Li*. He says, “According to the old system, a yojana consists of 40 Li ; according to the current practice of the administration in different parts, a yojana measures 30 Li ; but the scientific treatises regard a yojana as equal to 16 Li only.” According to St. Martin, the measure of one Li in China, in the 7th century A.D., was equal to 329 metres i.e. 1080 ft. by English measure**.