From NPD Books:
Annual print books unit volume in the U.S. reached 825.7 million, up 9%, or 67.8 million units, over the previous year. 2021 print volume was the highest ever seen in NPD BookScan, going back to the start of data tracking in 2004. This was the first time annual volume rose above 800 million units.
Total adult print book sales grew 11% over 2020, and adult fiction was the leading growth area in 2021. Adult fiction experienced the highest absolute unit gains of any supercategory for the year and contributed to more than half of total market gains, with 174 million units sold, 35 million more units than 2020. Adult non-fiction posted 323 million in sales and grew by 14 million. Top growth adult categories of the year included graphic novels, general fiction, romance, religion (NF), and business.