Floyd Mayweather Drops $1 Mil On Huge 5+ Lb. Chain From Johnny Dang

Floyd Mayweather just outdid himself (and everyone else, too), dropping $1 MILLION on a BIG ass iced-out, white gold chain that weighs nearly 6 pounds!!

45-year-old Mayweather linked up with Johnny Dang -- celeb jeweler and grill king -- and while the boxing legend has a birthday coming up, we're told he was just in the mood to treat himself,

And, did he ever ... with the biggest necklace in the world (as far as JD knows).

The chain, which weighs 2.6 kilos (or 5.7 lbs.), is made of white gold and has 8,500 diamonds -- a whopping 300 ct.'s -- and costs 7 figures!

On the clasp of the Cuban link chain, in diamonds, are the letters "TMT" ... for "The Money Team".

It's not the first time Mayweather has bought ridiculously expensive pieces from Dang ... but it's absolutely the biggest chain he's ever bought.

Of course, Floyd retired from fighting professionally years ago ... but TBE's still putting on exhibition fights across the globe. In fact, Mayweather's boxing Aaron Chalmers at the O2 in London on February 25 ... and you can bet he'll go home with another big check.