18mo

With dimensions of approximately 6.75" x 9.5" (170mm x 240mm), the 18mo format has a compact surface area around 64 square inches or 410 square cm. Also referred to as Eighteenmo, this book size gets its name from 18 leaves of paper being folded into one signature during old bookbinding practices. Falling between 16mo and 12mo in size, 18mo became popular for portable editions of literary fiction and nonfiction. The 6.75" x 9.5" size allowed books to remain lightweight and easily carried, while having a bit more text per page compared to 16mo. Especially common in the 19th century for condensed classics and travel books, 18mos were ideal for literature on-the-go. Originating from early printing press formats, the versatile 18mo size could comfortably fit around 225-300 pages printed on both sides. While less common today, 18mo remains useful for compact books when portability and condensing content down are key aims. Its success stems from striking a balance of travel-friendly compactness and smoothly readable formatting.