Which trim size should I choose for my book?

6 × 9 in is the industry default for trade paperbacks and works for almost any book — it's also BookyAI's default, so if you're unsure, leave it. Compact sizes (5 × 8 and 5.25 × 8) are common for mass-market and genre fiction; 5.5 × 8.5 suits novels and memoirs; 7 × 10 and 8.5 × 11 are for workbooks, manuals and large-print editions; A5 and A4 are the international (metric) equivalents commonly used outside the US. All eight options in BookyAI's trim selector are standard sizes accepted by Amazon KDP and other print-on-demand services.