Title Case vs Sentence case: which to use and the exact rules
Three style guides, three different answers, and the four-letter rule that separates them.
Sentence case capitalises the first word and proper nouns, nothing else: How to remove duplicates in Excel. Title Case capitalises the major words: How to Remove Duplicates in Excel. Which words count as major is where AP, APA and Chicago part company — AP capitalises all words of four letters or more, APA uses four or more, Chicago capitalises by part of speech regardless of length.
The rules side by side
| Question | AP Stylebook | APA 7th | Chicago 17th |
|---|---|---|---|
| Prepositions | capitalise if 4+ letters | capitalise if 4+ letters | lowercase, any length |
| Conjunctions (and, but, or) | lowercase if under 4 letters | lowercase if under 4 letters | lowercase always |
| Articles (a, an, the) | lowercase unless first | lowercase unless first | lowercase unless first |
| to in an infinitive | lowercase | lowercase | lowercase |
| Word after a colon | capitalise | capitalise | capitalise |
| Hyphenated compound | capitalise both parts | capitalise both parts | capitalise both unless second is an article or preposition |
| Last word of the title | capitalise | capitalise | capitalise |
Worked example. The title a guide to working with data from broken pdfs becomes:
- AP: A Guide to Working With Data From Broken PDFs — With and From are four letters, so they are capitalised.
- Chicago: A Guide to Working with Data from Broken PDFs — prepositions are lowercase whatever their length.
- Sentence case: A guide to working with data from broken PDFs.
That single difference — With against with — is the fastest way to tell which guide a publication follows.
Where each one belongs
Sentence case is now the default for interface text, buttons, form labels, error messages, email subject lines and most product documentation. Google, Apple, Microsoft and GOV.UK all specify it in their style guides. It reads faster because capitals inside a line slow the eye, and it degrades gracefully when a label gets truncated.
Title Case belongs on book titles, article titles in a bibliography, newspaper headlines, and the names of things — courses, chapters, legal documents. It signals this is the name of a work, which is exactly what you want in a reference list.
Two smaller conventions worth fixing once. Bibliography entries in APA use sentence case for the article title and Title Case for the journal name, in the same line — that is deliberate, not an error. And German capitalises every noun in running text regardless of headline style, so a converter run over German copy will damage it; case rules are language-specific and no tool guesses the language for you.
The awkward middle ground is web page titles and H1s. There is no ranking difference either way. Sentence case tends to look less like an advertisement in search results and takes up fewer pixels, which matters when the desktop title cut-off is around 580 pixels. Title Case looks more authoritative in a magazine context. Pick one, write it in the style guide, and apply it everywhere — inconsistency is what actually looks unprofessional.
Three cases people confuse with these two
- ALL CAPS. Not a case style, an emphasis style. Reading speed drops measurably because word shape disappears, and screen readers may spell out short capitalised strings letter by letter. Never use it for body text or for more than a few words.
- Start Case. Every single word capitalised, including a, the and of. This is what most naive converters produce, and it is not correct in any major style guide. It is fine as a mechanical transformation for column headers, not for a headline.
- Small caps. A typographic effect, not a text transformation. If you type capitals to fake it, the text is capitals for search, copy-paste and screen readers. Use the font feature instead.
An automatic case converter gives you Title Case, Sentence case, UPPERCASE, lowercase and inverse in one paste, which covers the mechanical part. The judgement calls below still need a human.
What usually goes wrong
- Acronyms flattened. Sentence case conversion turns PDF into Pdf and NASA into Nasa. Any converter does this; check acronyms by eye afterwards, every time.
- Proper nouns lowercased. Excel, Google, iPhone. The iPhone case is worse — both Title Case and Sentence case want to make it IPhone.
- Everything capitalised. The Best Way To Remove Duplicates In Excel capitalises To and In, which no style guide allows. That is Start Case wearing a costume.
- Sentence detection failing on abbreviations. A converter splits at every full stop, so e.g. this one becomes e.g. This one.
- Mixed styles in one list. A blog index where half the titles are Title Case is more distracting than either style on its own.
- Hyphenated compounds handled inconsistently. State-of-the-Art or State-of-the-art? AP and APA say capitalise both meaningful parts; be consistent within a document.
A workable house rule
If you do not have a style guide, this covers almost everything and produces no arguments:
- Sentence case for everything on screen: navigation, buttons, labels, headings, H1s, page titles, email subjects.
- Title Case for the names of published works when you cite them, following Chicago — prepositions and conjunctions lowercase, everything else capitalised.
- Acronyms keep their own capitalisation in both.
- Never ALL CAPS beyond three words.
- The first word after a colon is capitalised in both styles.
Write it down in four lines like that and the arguments stop. The version that fails is the unwritten one, where each writer applies the guide they learned at a previous job and the blog index ends up with three styles in twelve rows.
Applying it to an existing site is a bulk job: export the titles one per line, run them through a converter, then read down the list for acronyms and product names. Sorting the list with a line sorter first groups similar titles together and makes inconsistencies jump out. Remember that changing a title does not change the URL slug, and it should not — slugs are lowercase regardless of which case style the title uses.
Related tools
Frequently asked questions
Title Case capitalises the major words of a title. Sentence case capitalises only the first word and any proper nouns, exactly like an ordinary sentence.
In AP and APA yes, because it has four letters. In Chicago no, because it is a preposition and Chicago lowercases prepositions of any length.
Either is correct. Sentence case is now the default for web and product interfaces; Title Case is standard for print headlines and cited work titles.
No. Neither style affects ranking. Sentence case is slightly narrower in pixels, which helps a long title fit inside the search result cut-off.
Capitalising every word without exception, including a, the and of. It is what naive converters produce and no major style guide accepts it for headlines.
Sentence case conversion lowercases everything after the first letter and cannot tell an acronym from an ordinary word. Fix acronyms by eye after converting.