In a report entitled "Fatal Journeys", the agency called on authorities to ensure the missing are identified and their families traced.
The estimated toll includes a record 5,400 migrants believed to have died in 2015 trying to cross borders, and a further 3,400 who have perished already this year, the IOM said.
Of last year's deaths, 3,770 occurred in the Mediterranean where boats capsized en route to Europe. Others died in the Bay of Bengal and Andaman Sea, the Gulf of Aden and Red Sea and along the US-Mexico border, it said.
"Something in the region of 60,000 migrants across the world have died over the last 20 years," Frank Laczko, director of IOM's global migration data analysis centre, told a Geneva news briefing by telephone from Berlin.
