Play video content EXCLUSIVE Showtime

Floyd Mayweather is expecting to make more than $300 MILLION from his fight with Conor McGregor ... which would break down to more than $8 MILLION per minute in the ring.

The boxer spelled it all out for Showtime's "All Access: Mayweather v. McGregor" -- explaining why no other professional athlete in the world is more bankable.

"I mean, am I the highest-paid athlete out there? And just coming back? We not talking about no contract. We not talking about no contract for no 4 years, or no contract for no 5 years. I can do it in 36 minutes. $300 (million) or better. In 36 minutes."

Not a bad deal.