Standard Book Sizes UK: Paperback, Hardback and A5 in mm, cm and Inches
UK book sizes in mm, cm and inches: A-format 111 × 178 mm, B-format 129 × 198 mm, Demy 138 × 216 mm, Royal 156 × 234 mm, A5 148 × 210 mm, and which Amazon KDP size matches each one.