Joachim Low's side booked their spot in Sunday's final with Argentina by thrashing Brazil 7-1 on Tuesday night, and Mertesacker believes that the number of options on offer to the manager has made the difference.
"We have one of the strongest squads I've ever played in," the Arsenal centre-back told reporters. "We have two excellent players for every position and everyone believes in each other.
"We have created excellent team spirit during the tournament and with those magnificent players growing up together it makes it easier."
Mertesacker may have to settle for a place on the bench this Sunday after being used as a substitute against Brazil.