Miller also weighed in at 156 pounds.
The UFC on Fox 3 main event will be held Saturday night at Izod Center, where the weigh-ins also took place.
Henderson, the former WEC champion, will be making his first defense of the UFC 155-pound title he took from Edgar on Feb. 26 in Saitama, Japan.
Diaz put himself in title contention by putting together a two-fight win streak since his return to the lightweight division Sept. 24 against Takanori Gomi. Diaz won that fight by first-round submission.
In his most recent outing, Diaz (15-7) overwhelmed Donald Cerrone en route to a unanimous decision Dec. 30 at UFC 141.
Though a title shot is on the line, Diaz expressed having too much respect for Miller to look ahead.
"He's tough," Diaz said. "He's a very good opponent."
Miller (21-3) was on the fast track toward a title shot until dropping a unanimous decision to Henderson on Aug. 14. He rebounded on Jan. 20 by submitting Melvin Guillard in the first round.
"This is a huge fight for two of the baddest men on the planet," Miller said.
Welterweight contender Johny Hendricks, who can earn a title shot with a victory in the co-main event, weighed in at 170½ pounds. Hendricks had the removed his shorts to make weight after initially tipping the scale at 171½.
His foe, former top contender Josh Koscheck, weighed 170½ pounds on his first attempt.
Every other fighter on the main card made weight.
Preliminary-card participant John Lineker failed to make the 126-pound mandatory limit for a nontitle flyweight bout, coming in at 127.
He was originally given two hours to lose the additional pound. But after being examined by a New Jersey State Athletic Commission physician, Linker was not allowed to shed any weight.
Linker has been allowed to compete Saturday night, but he forfeited 20 percent of his purse to opponent Louis Gaudinot (126 pounds).