Title Case Rules: What AP and Chicago Style Actually Capitalize
AP style capitalizes every word of four or more letters in a title, plus all verbs regardless of length, while lowercasing shorter articles and prepositions (a, an, the, to, in, for) unless they start or end the title. Chicago style uses a similar approach but capitalizes prepositions of five or more letters instead of four, and additionally capitalizes the conjunctions "yet" and "so," which most style guides lowercase.
A simple Title Case converter that capitalizes every single word is a genuinely different thing from editorial title case, and knowing the gap matters the moment you're formatting a headline or citation that needs to match a specific style guide.
Simple Title Case vs. editorial title case
A basic Title Case converter capitalizes every word without exception — the screenshot above shows "To" capitalized, which is exactly what a simple converter is supposed to do, and exactly what AP and Chicago style would correct. That's not a bug in either version; they're solving different problems. Simple Title Case is a formatting default; editorial title case is a set of house-style rules built for headlines, book titles, and citations.
If you only need something that reads as "title-like" — a page heading, a casual project name — simple Title Case is fine as-is. If the text needs to match a publication's actual style guide, the short words need manual correction afterward.
The core rule both styles share
Both AP and Chicago capitalize the first and last word of a title no matter what it is, plus all nouns, verbs, adjectives, adverbs, and pronouns throughout. The disagreement is specifically about short articles, conjunctions, and prepositions in the middle of a title — a, an, the, and, but, or, to, in, on, at, and similar words.
AP's rule is a clean length cutoff: capitalize any word of four or more letters, full stop, even if it's a preposition that would otherwise be lowercased — "With" and "From" get capitalized under AP because they clear four letters, while "to" and "in" stay lowercase.
Where Chicago diverges from AP
Chicago's cutoff for prepositions sits at five letters instead of AP's four, so a word like "with" (four letters) stays lowercase under Chicago but would be capitalized under AP. Chicago also capitalizes the coordinating conjunctions "yet" and "so," which AP and most other style guides lowercase along with the rest of the short conjunctions.
These are small differences in practice, but they're exactly the kind of detail that makes a title look inconsistent if half your titles follow one style guide and half follow the other without anyone deciding which.
Convert, then adjust for your style guide
Our Case Converter generates simple Title Case instantly alongside ten other casings. For AP or Chicago-specific title case, use it as the starting point and manually lowercase the short articles, conjunctions, and prepositions your style guide calls for — a much faster edit than capitalizing a title by hand from scratch.