Froch tipped the scales at 11 stone 13 pounds and eight ounces for the feature bout at Nottingham's Capital FM Arena, where he won the title with a superb fifth-round stoppage of Lucian Bute in May.
Mack, from Philadelphia, had to remove his underpants after initially weighing a few ounces over the 168 pound limit.
Mack has a record of 31-4-2 with 17 career knockouts.
The 32-year-old's notable bouts include victories over Daniel Judah (brother of Zab) and Otis Griffin, with defeats coming in well-received contests with Librado Andrade, Glen Johnson and the undefeated Tavoris Cloud.
Matchroom promoter Eddie Hearn said: "Carl is focused solely on this fight, nothing else. He is not looking beyond the dangerous threat of Mack. I take care of that side of things.
"Carl likes a fight but is intelligent too and puts on a great show. This will be no different.
"The British public get behind him as their number one fighter and when he steps into the ring, he puts everything on the line.
"Mack will find that out and that is why Carl is such a special fighter."
The undercard is spearheaded by Tony Bellew and the 29-year-old had to be separated from Argentine opponent Roberto Bolonti at the weigh-in for their WBC Silver light heavyweight title bout.
- Sports & Recreation