NEW YORK — (CNN) Donald Trump estimated on Tuesday that it will cost about $8 billion to build the wall he has promised to erect on the U.S.’s southern border if elected president.

Trump has vowed to force Mexico to pay for the border wall and said Tuesday on MSNBC that the hefty $8 billion price tag “is a tiny fraction of the money that we lose with Mexico” on trade.

“The wall is probably $8 billion, which is a tiny fraction of the money that we lose with Mexico. We lose a tremendous amount of trade deficits. We have a trade deficit with Mexico that is astronomical, much bigger than that. We will get — and I say it also is also part of my plan — Mexico is going to play for the wall,” he said.

Trump’s proposal to build a wall on the U.S.’s southern border and his hardline immigration policies have become central to the billionaire’s presidential campaign. But Tuesday marked the first time he has tacked a specific dollar amount to his border wall proposal.

Trump said he came up with the figure by “multiplying the number of miles by a certain number.”

“I’m taking price per square foot and price per square, you know, per mile, and it’s a very simple calculation,” Trump said, noting that he would need to erect about 1,000 miles of border wall along the 2,000-mile long border because of natural barriers along certain parts.

Trump’s pledge to make Mexico pay for the wall drew harsh criticism just days earlier from former Mexican President Felipe Calderon.

“Mexican people, we are not going to pay any single cent for such a stupid wall, and they need to know that,” Calderon had said. “And it’s going to be completely useless.”

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