Logan Paul and Floyd Mayweather hopped on the scales Saturday ... and the weigh-in was a well-produced, splashy show, featuring music, commentary, a huge crowd and lots of smack talk.

The weigh-in went down in Miami ... the prelude to the pay-per-view match which goes down Sunday night in Miami Gardens.

Logan Paul weighed in at 189.5 pounds ... barely under the maximum of 190. Mayweather came under the 160 lb limit at 155. There's also a 6-inch height difference in favor of Logan.

Logan entered to “Sweet Child O’ Mine” by Guns N' Roses. He said his presence “proves this sh*t is a simulation.” And then, he went on ... “None of it’s real. The aliens are coming in June. Just be ready. Tomorrow, I break the f***ing simulation and beat the greatest boxer in the history of the planet.”

As for Floyd ... his message is simple as he yawned at Paul's presence ...“Height don’t win fights,” he said. “Weight don’t win fights. Fighting wins fights, and at the end of the day, I can fight.”

The fight has drawn massive interest, both inside and outside the boxing world, thanks in big part to Logan's showmanship. Check out the video he dropped Saturday night ... fueling even more interest in the fight.

It's pretty crazy ... Mayweather's 50-0, and Paul is 0-1, so it seems ridiculous on its face.  But, boxing is full of surprises, so ya never know.

Mayweather says he's gonna pocket $100 mil from the fight.