Title case converter — four style guides, one headline.

Paste a headline and switch between AP, Chicago, APA and MLA to see the same line capitalised four ways. The rules genuinely differ, and this page shows where — word by word, with the source each rule comes from.

85 characters70 without spaces16 words2 lines

Everyday cases

Developer cases

Title Case style guide

Use the superseded CMOS 17 preposition rule (lowercase every preposition — this reverts the preposition rule only, not everything the 18th edition changed)

Chicago Manual of Style, 18th edition (2024). Lowercase prepositions of four letters or fewer, except when used adverbially or adjectivally; capitalise prepositions of five letters or more. First word always capitalised; last word always capitalised.

Judgment calls — 1 word a converter cannot settle

over — Lowercased as a preposition. Capitalise it under every guide if it is the particle of a phrasal verb ("Back Up", "Log In").

Keep NASA, iPhone as typedTurkish i rules

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The one question the guides answer differently

Every style guide agrees about most of a title. Nouns, verbs, adjectives, adverbs and pronouns get capitals; a, an and the do not, unless they open the title. If titles were made only of those, there would be one title case and no need for this page.

The disagreement is about prepositions, and it reduces to a single question: does a word earn its capital by being long, or by being an important part of speech?

AP and APA are length guides. Count the letters: four or more, capitalise. This is easy to apply and easy to check, which is exactly why a newsroom uses it. It also means With, From, Into and Over — all plainly prepositions — get capitals, because they happen to be four letters long.

Chicago and MLA are word-class guides. A preposition is a minor word and stays lowercase because of what it is, not how long it is. MLA holds that line absolutely: between, through, without and against are lowercase mid-title however long they get. Chicago held the same line until 2024, when its 18th edition introduced a floor — prepositions of five letters or more now take a capital — which puts current Chicago in the middle of the two camps and leaves MLA alone at the far end.

Thirty minor words, in every guide, in one table

Below is the actual behaviour of this converter for the thirty words that decide most titles. Each word was run through the tool inside the carrier phrase the report WORD a study so that it sits in the middle of a title, where no first-word, last-word or after-colon rule can reach it. What you see is the pure word-class result.

15 of the 30 words come out differently depending on the guide, and 7 of those splits are four-letter prepositions — the exact length band where the length guides and the word-class guides part company.

Mid-title capitalisation by guide. Generated by running each word through this page’s converter inside a carrier phrase, so every cell is the tool’s real output and none of it was summarised by hand.
Word	Letters	Word class	AP	Chicago 18	APA 7	MLA 9
a	1	article	a	a	a	a
the	3	article	the	the	the	the
of	2	preposition	of	of	of	of
to	2	preposition / infinitive marker	to	to	to	to
up	2	preposition / particle	up	up	up	up
and	3	coordinating conjunction	and	and	and	and
but	3	coordinating conjunction	but	but	but	but
for	3	coordinating conjunction / preposition	for	for	for	for
nor	3	coordinating conjunction	nor	nor	nor	nor
yet	3	coordinating conjunction	yet	Yet	yet	yet
off	3	preposition / particle	off	off	off	off
with	4	preposition	With	with	With	with
from	4	preposition	From	from	From	from
into	4	preposition	Into	into	Into	into
over	4	preposition	Over	over	Over	over
like	4	preposition	Like	like	Like	like
than	4	preposition / subordinator	Than	than	Than	than
upon	4	preposition	Upon	upon	Upon	upon
about	5	preposition	About	About	About	about
after	5	preposition / subordinator	After	After	After	after
among	5	preposition	Among	Among	Among	among
under	5	preposition	Under	Under	Under	under
between	7	preposition	Between	Between	Between	between
through	7	preposition	Through	Through	Through	through
without	7	preposition	Without	Without	Without	without
because	7	subordinating conjunction	Because	Because	Because	Because
when	4	subordinating conjunction	When	When	When	When
is	2	verb	Is	Is	Is	Is
be	2	verb	Be	Be	Be	Be
it	2	pronoun	It	It	It	It

Three patterns fall out of that table. Words of three letters or fewer are safe — every guide lowercases them, so of, to, and and the never cause an argument. Words that are not minor words at all are equally safe: is, be and it are two letters and every guide capitalises them, because a verb is a verb and a pronoun is a pronoun regardless of size. Everything contentious lives in the middle band, from four letters up.

The yet row is the one deliberate oddity, and it is worth explaining out loud. MLA names all seven coordinating conjunctions — for, and, nor, but, or, yet, so — as lowercase. Chicago’s rule names five: and, but, for, or, nor. This converter follows each guide’s own list and does not assume Chicago meant to include the other two, which is why Yet is capitalised in the Chicago column and lowercase everywhere else. Secondary summaries of Chicago disagree with each other on this point; we follow the wording the manual’s publisher and the most consistent secondary reproductions give. Because this is a genuine disagreement and not a settled rule, so and yet are named in the amber Judgment-calls panel under the buttons whichever guide you choose — including when Chicago capitalises them.

The rules, and where each comes from

The four rule sets as published, with the source each one is taken from. Where a clause cannot be applied without parsing the sentence, the converter flags the word rather than encoding a guess.
Guide	Basis	Preposition rule	Last word of title	Source
AP (Associated Press Stylebook)	length	Capitalise prepositions and conjunctions of four letters or more.	Always capitalised	AP Stylebook, “composition titles” entry (wording of the 54th ed., 2019, onward); read from archived copies of the entry, never from a live subscription
Chicago Manual of Style, 18th edition (2024)	word class	Lowercase prepositions of four letters or fewer, except when used adverbially or adjectivally; capitalise prepositions of five letters or more.	Always capitalised	CMOS 18th ed. §8.160 — the section text is paywalled; encoded from the publisher’s own online guidance (Chicago Manual of Style Online Q&A, “Capitalization, Titles”) and the most consistent secondary reproductions
APA 7th edition	length	Capitalise every word of four letters or more, prepositions included.	No such rule — follows the normal test	APA Style, “Title case capitalization”, apastyle.apa.org — the publisher’s own free guidance page, read directly
MLA Handbook, 9th edition	word class	Lowercase every preposition regardless of length.	Always capitalised	MLA Handbook 9th ed. §2.90 — the section text is paywalled; encoded from the publisher’s own online guidance and the most consistent secondary reproductions

Chicago’s preposition rule carries two clauses the converter cannot execute, and they are in the table because they belong to the rule itself and not to a footnote under it. A preposition used adverbially or adjectivally keeps its capital at any length — that is grammar, not spelling, so the word is flagged instead of guessed. And Chicago makes it optional to capitalise a short preposition when it is paired with a longer one, which is a choice a tool cannot make on your behalf. Both are decisions for the human holding the style sheet.

One headline that trips both thresholds

Take notes from the bridge between two worlds. It contains a four-letter preposition and a seven-letter one, so it exercises both thresholds at once:

AP: Notes From the Bridge Between Two Worlds
Chicago 18: Notes from the Bridge Between Two Worlds
APA 7: Notes From the Bridge Between Two Worlds
MLA 9: Notes from the Bridge between Two Worlds

AP and APA capitalise both prepositions. Chicago capitalises the seven-letter one and not the four-letter one. MLA capitalises neither. Three different headlines from one input, and all three are correct — for their guide.

What the converter refuses to guess

A few sub-rules turn on grammar, where spelling is no help at all, and a converter that pretends otherwise is just wrong quietly. When the output contains one of these words, an amber panel appears under the style-guide buttons naming it. The full list of what this tool will not decide:

Is "up" in “Backing Up Your Laptop” a preposition or the adverbial particle of a phrasal verb? All four guides capitalise an adverbial particle. Deciding which one it is needs a parser, so CaseConv applies the preposition reading (lowercase) and flags the word under “Judgment calls” for you to fix.
Does AP capitalise “to” when it marks an infinitive — “How To Win” or “How to Win”? It does, and this one is not in dispute: AP’s composition-titles entry explicitly capitalises “to” in infinitives — “What I Want To Be When I Grow Up.” Telling an infinitive marker from a preposition still needs a parser, so CaseConv lowercases mid-title “to” under every guide and flags it for you to fix. Chicago and MLA lowercase it either way.
Does Chicago lowercase “so” and “yet”? Chicago’s rule names exactly five coordinating conjunctions — and, but, for, or, nor — and “so” and “yet” are not among them, so CaseConv capitalises them under Chicago. MLA names all seven FANBOYS, so MLA lowercases them. Secondary summaries of Chicago disagree with each other here; we follow the wording the manual’s publisher and the most consistent secondary reproductions give, and flag both words whichever guide you pick.
Does AP capitalise the first word of a subtitle after a colon? AP publishes no rule for subtitles inside a composition title, so there is no AP text to follow. APA, Chicago and MLA all capitalise it, and AP’s own published copy does the same, so CaseConv extends that shared behaviour to AP and invents no AP-specific exception.

None of these is a limitation of this tool specifically — no rule-based converter can settle them, because the information needed is not in the letters. The difference is whether the tool tells you.

Practical notes

Paste all your headings at once. The converter treats each line as its own title, so first-word and last-word rules apply per line. Forty headings in, forty consistently capitalised headings out — which removes the failure that readers actually notice, two headings on one page following two different guides.

Brand casing survives. With Keep NASA, iPhone as typed ticked, any word you deliberately cased — an acronym, iPhone, eBay, McDonald’s — is left exactly as you typed it. Untick it if you are re-casing a heading that is currently in full caps and want everything reconsidered from scratch.

A title in ALL CAPS is folded first. A line with no lowercase letters carries no case information worth keeping, so the converter lowercases it before applying the guide. Paste THE STATE OF THE ART and you get a properly capitalised title back instead of the same shouting.

Title case questions

What is title case?

Title case is the convention of capitalising the important words of a heading and leaving the minor ones lowercase — The Sound and the Fury, not The sound and the fury and not The Sound And The Fury. It is not the same as capitalising every word (that has no name and no style guide behind it) and not the same as sentence case, which capitalises only the first word.

Which words are capitalised in title case?

All four guides capitalise nouns, pronouns, verbs (including two-letter ones like is and be), adjectives and adverbs, plus the first word of the title and of any subtitle. All four lowercase the articles a, an and the mid-title. The disagreement is entirely about prepositions and about whether the final word gets special treatment.

Is “with” capitalised in a title?

It depends on the guide, and this single word is the cleanest illustration of the split. With is a four-letter preposition. AP and APA capitalise anything four letters or longer, so both write Gone With the Wind. Chicago lowercases prepositions of four letters or fewer and MLA lowercases prepositions of any length, so both write Gone with the Wind.

Should the last word of a title always be capitalised?

Under AP, Chicago and MLA, yes — all three state that the final word takes a capital whatever it is. Under APA, no: its published rule list has no last-word clause, so a title ending on a short preposition ends lowercase. What Are You Waiting For in three guides, What Are You Waiting for in APA.

Do I capitalise the word after a colon?

Yes. APA capitalises the first word after a colon explicitly; Chicago and MLA reach the same result through the rule that the first word of a subtitle is capitalised. AP publishes no rule for subtitles inside a composition title — but AP’s own published copy capitalises the word after the colon, articles included, so this converter applies the shared behaviour to AP rather than inventing an exception for it.

How do hyphenated words work in title case?

Each element is judged on its own: capitalise the first, then capitalise the rest unless they are articles, prepositions or coordinating conjunctions. That gives Four-Day Week and Self-Report Measure, but Step-by-Step Guide with a lowercase by in the middle. Chicago and APA state this explicitly; AP does not address hyphenation in titles, so the converter applies the shared behaviour to AP too. It is not a guess about AP: asked how to capitalise Easy-to-Care-for Perennials as a composition title, AP’s editor answered “As you have it” (AP Ask the Editor, May 11, 2020) — the same per-element test. Chicago itself moved in its 18th edition, which now capitalises the element after a prefix: Anti-Intellectual, E-Commerce, T-Shirt, X-Ray.

Which title case does my publisher want?

Ask, and if nobody knows: AP for journalism, press releases and web marketing; Chicago for books and general non-fiction; APA for psychology, education and the social sciences; MLA for literature and languages. Consistency matters more than the choice — paste all your headings in at once so a single guide is applied to every one of them.

Keep going

All twelve case converters on one page — the full tool, with the four title-case style guides and the six programmer cases side by side.
Sentence Case Converter — the other convention for headings — one capital, at the start, and academic publishers increasingly prefer it.
Uppercase Converter — when a heading has to shout, and what that does to your character count.
Camel Case Converter — the developer equivalent of this page: which identifier case each language expects.
Word Counter — our sister tool for the other half of the job: word, character and reading-time counts when you are writing to a limit instead of fixing capitalisation.