How many preludes and fugues are included in each book of The Well-Tempered Clavier?

Each book of The Well-Tempered Clavier by Johann Sebastian Bach contains 24 preludes and 24 fugues, for a total of 48 pairs across the two volumes.1

The collection is organized as follows:

• Book I: Completed in the 1720s, this volume includes 24 preludes and 24 fugues, covering all 12 major and 12 minor keys.1
• Book II: Completed approximately two decades later, this volume also contains 24 preludes and 24 fugues, again exploring all 12 major and 12 minor keys.1

These works were designed as pedagogical exercises to help keyboard players master chords, scales, and arpeggios in every key.1