Metallica became the first album of the SoundScan era to pass 16 million copies sold in the United States.
Nielsen SoundScan began tracking U.S. music sales in 1991, the same year Metallica was released. The album's sustained performance made it much more than an early-1990s hit: it continued selling steadily across CDs, cassettes, downloads, and later formats.
By 2016, the album had sold about 16.4 million copies in the United States according to the figures summarized in its article. Cassettes alone accounted for approximately 5.8 million of those sales, showing how important that format was during the album's original era.
The milestone is distinct from the album's later certification history. The Recording Industry Association of America certified Metallica 2× Diamond in 2025 for U.S. shipments of 20 million copies.