The Compositor's Art: Casting Off a Manuscript
Before a word reached print in the Victorian era, it had to pass through the hands of a compositor — the master craftsman who set type by hand into a metal galley. Before touching a single piece of lead type, they performed a ritual called casting off: estimating how many pages the manuscript would fill. This was not a guess. It was an exact calculation based on column width (the "measure"), font size, and line leading (spacing). A skilled compositor could predict page count to within half a page before setting a single line.
The standard of 500 words per single-spaced page emerged from this tradition. Typographers in the 1880s discovered that a 12-point Roman typeface on an octavo page with 1-inch margins consistently yielded approximately 500 words per column. This became the compositor's fundamental unit — the "galley measure." Double-spaced manuscripts (needed for editorial correction marks to fit between lines) yielded exactly half: 250 words per page.
Why Format Changes Everything
A novel and an academic paper with identical word counts produce dramatically different page counts — because they follow entirely different typographic conventions. A trade paperback uses a smaller page (6×9"), tighter leading, and 11-point serif to maximise density at approximately 300 words per page. A US screenplay uses Courier 12pt with wide margins and format-specific rules (scene headers, action lines, dialogue indents) that drop density to roughly 185 words per page — which is why "one page = one minute of screen time" is a reliable rule of thumb.
E-books add another variable: screen pagination is device-dependent. The industry average for a typical Kindle at default settings is roughly 180 words per screen page. This is why e-book publishers focus on word count rather than page count when quoting manuscript length — page count is meaningless when every reader controls their own font size.
Reading the Chart
The bar chart above shows all five formats simultaneously, scaled proportionally. The tallest bar is always the format that produces the most pages from your word count — usually double-spaced, because it has the fewest words per page. The shortest bar is whichever format packs the most words onto a page. This at-a-glance comparison was exactly what a Victorian compositor provided to an author who asked: "How long will my book be?"