Short answers, pulled from the story.
A folio book measures roughly half the size of the original sheet because a printer in London folded a full sheet once to create two leaves. This single fold defined what bibliographers call a folio and determined the final dimensions before binding occurred.
An octavo demands three folds total where each fold reduces the leaf size by half again. Printers arranged text on both sides of large sheets and cut open the edges with knives if the reader did not trim them themselves.
By the year 2003, publishers no longer relied on folding techniques to define book sizes. A modern novel might contain sixteen leaves but originate from a sixty-four-page sheet using perfect binding that glued every leaf directly into the spine without any folding.
A Penguin Classics paperback in the United Kingdom measures B-format dimensions which contrasts with A-format being slightly narrower than ISO B6. Australian publishers use similar standards except C-format becomes larger there and they also introduced a B+ format for specific editions.
The Guinness World Records listed Bhutan: A Visual Odyssey Across the Last Himalayan Kingdom as the largest published book in 2003 measuring three meters tall. Michael Hawley created this volume while another record holder emerged in 2012 when Dubai produced This the Prophet Mohamed at four meters high.