Capitalization is the most argued-about detail in written English, and most of the argument comes from people applying different systems without realising it. This guide covers every style, what the major guides specify, and how to choose.

The five capitalization styles

Style	Example	Use it for
Sentence case	The quick brown fox	Prose, UI copy, modern headings
Title Case	The Quick Brown Fox	Headlines, book and article titles
Capitalized Case	The Quick Brown Fox	Names, labels, spreadsheet columns
UPPER CASE	THE QUICK BROWN FOX	Short labels, legal disclaimers
lower case	the quick brown fox	URLs, usernames, data normalisation

Title Case and Capitalized Case look identical until a short word appears. Title Case keeps of, the, and and lowercase in the middle; Capitalized Case capitalises everything. That single difference is behind most capitalization mistakes in published writing.

The rules that never change

Regardless of style guide, always capitalise:

The first word of a sentence.
Proper nouns — names of people, places, organisations, brands.
The pronoun I.
Days, months, and holidays — but not seasons.
Languages and nationalities — English, Turkish, Brazilian.
Titles before a name — President Lincoln, but "the president spoke".

These are grammar, not style. No guide disagrees.

Where the style guides diverge

The disagreement is almost entirely about which short words get capitalised in a title. AP and APA use a length rule — four letters or more gets a capital. Chicago and MLA lowercase all prepositions regardless of length.

So the same headline is legitimately A Guide Over the Bridge in AP and A Guide over the Bridge in Chicago. Neither is wrong.

The full comparison, including the edge cases that trip up phrasal verbs and hyphenated compounds, is in Title Capitalization: AP vs Chicago vs APA.

Title case or sentence case for headings?

This is the practical decision most teams face, and the answer has shifted. Most software companies and a growing number of publications now use sentence case for headings, buttons, and documentation.

Sentence case reads faster, has no edge cases to argue about, and translates cleanly into languages with no title case at all. Title case remains standard for article headlines, book titles, and academic paper titles.

The full argument, including when title case is still correct, is in Title Case vs Sentence Case.

Why all caps is harder to read

We partly recognise words by their outline shape — the pattern of ascenders and descenders. Capitals flatten every word into an identical rectangle, removing that cue, which measurably slows reading.

Use capitals for short bursts: a heading, a label, a warning. Never for body text. Online, a full sentence in capitals also reads as shouting, which is rarely the tone intended.

If you have inherited a document in capitals, converting it back is a two-minute job — see How to Fix Text You Accidentally Typed in All Caps.

What automatic conversion cannot do

Worth being clear about the limits, because every capitalization tool shares them:

Proper nouns are lost. Converting to sentence case lowercases everything first, so names, places, and brands need restoring by hand. No rule can distinguish "apple the fruit" from "Apple the company" without understanding the sentence.
Names with internal capitals break. McDonald becomes Mcdonald, O'Neill becomes O'neill.
Phrasal verbs are ambiguous. "Look Up the Answer" capitalises up; "Walk up the Hill" does not. Same word, different job.
Acronyms may be flattened. NASA can become Nasa depending on the conversion.

The practical workflow is convert, then scan. Seconds of checking against minutes of manual editing.

Capitalization for specific contexts

URLs — always lowercase. Many servers are case-sensitive, so /About and /about can become duplicate pages. See URL slug best practices.
Email addresses — the domain is case-insensitive; treat the whole thing as lowercase for storage and comparison.
Code — governed by naming conventions rather than English grammar. See the naming conventions guide.
Data columns — normalise to one case before importing, or "London" and "LONDON" become two categories.

The rule that matters most

Pick one style and apply it everywhere. Inconsistent capitalization across a site is far more visible — and looks far more careless — than any particular choice. Nobody has abandoned a page because it used Chicago rather than AP. Plenty have noticed three headings capitalised three different ways.

Write the decision down, including which guide you defer to for edge cases, and make it the default in your CMS.

Tools in this cluster

Sentence case converter — normalise messy or all-caps text
Title case converter — apply editorial headline rules
Capitalize each word — proper case for names and labels
Uppercase to lowercase and lowercase to uppercase
aLtErNaTiNg cAsE — the mocking meme font

The Complete Guide to Text Capitalization