Mayweather vs. McGregor Is Official, 12 Rounds Boxing

2:46 PM PT -- TMZ Sports spoke with Dana White who says the fight will be a 12 round boxing match. Both guys will use 10 ounce gloves. They will fight at 154 pounds.

The fight will take place at the T-Mobile Arena. Ticket prices have not been set yet.

There WILL be an undercard -- it will be boxing and Mayweather Promotions will handle the matchmaking.

We asked Dana if there was a possibility Roy Jones Jr. will fight Anderson Silva -- he told us, "I highly doubt it."

Both Floyd and Conor will be tested by USADA for performance enhancing drugs.

Dana says he expects Conor to make around $100 million for the fight but wouldn't break down the financials.

Dana says he spoke with Conor Wednesday morning -- he's VERY excited. Conor also believes with all his heart he will knock Mayweather out.

IT'S HAPPENING!!!

Floyd Mayweather has signed his deal and will box Conor McGregor on August 26.

Dana White was leading the negotiations for the UFC -- and had vowed to strike a deal with Floyd's camp. Now, the two sides have reached an agreement, as first reported by Yahoo Sports.

Conor and Floyd will square off in Vegas.

Conor posted about the fight on Instagram -- saying, "The fight is on." He replaced Floyd's pic with a shot of Floyd Sr.

Conor has said he expects to make more than $100 MILLION from the fight. Floyd has said he wanted double or triple that. No word on the exact details.

The last time we spoke with Floyd, he laid out exactly why he thinks Conor has a real shot to beat him.