Question: what are the book sizes for kdp?
Answer: IngramSpark and KDP Print trim size availability.
IngramSpark. 4 × 6 inches (154 × 102mm) 4 × 7 inches (178 × 102mm) 4.25 × 7 inches (178 × 108mm) 4.37 × 7 inches (178 × 111mm)/ A. ... 
Amazon KDP Print. 5 × 8 inches (12.7 × 20.32 cm) 5.06 × 7.81 inches (12.9 × 19.8 cm) 5.25 × 8 inches (13.335 × 20.32 cm)