Stephenson 2- 18 is the largest star in the universe. The diameter of Stephenson 2-18 is approximately 2,990,684,400 kilometers. And it's about 2,150 times the size of the sun. credit: TheBinduOrder Data World Copyright Disclaimer: - Under section 107 of the copyright Act 1976, allowance is mad for FAIR USE for purpose such a as criticism, comment, news reporting, teaching, scholarship and research. Fair use is a use permitted by copyright statues that might otherwise be infringing. Non- Profit, educational or personal use tips the balance in favor of FAIR USE.