Adele's album 25 sold 3.38 million copies in its first week in the United States. That figure refers to pure album sales, not the broader total of album-equivalent units that also included track sales and streaming.
Released on 20 November 2015, 25 debuted at number one on the Billboard 200. Its first-week performance was extraordinary: it became the first album tracked by Nielsen SoundScan to sell more than three million copies in a single week. It also surpassed the previous record held by *NSYNC's No Strings Attached, which sold about 2.42 million copies in 2000.
A common mix-up is the nearby figure of 3.48 million. That number represents album-equivalent units, while 3.38 million is the pure-sales total asked for in the question. The distinction matters because chart reporting combines purchases with equivalent activity from downloads and streams.
The album's success was helped by the worldwide popularity of its lead single, “Hello,” and by Adele's decision to keep 25 off major streaming services at release. The album eventually became one of the best-selling records of the 2010s.