Which Letter Case Goes Where? A Practical Cheat Sheet

Capitalization looks like a detail until it's inconsistent. One heading in Title Case, the next in sentence case, a button in ALL CAPS, and a page starts to feel careless, even if nobody can say exactly why. Most of the time, the problem isn't knowing how to capitalize. It's knowing which case belongs where.

This is the cheat sheet I wish I'd had: what each common case is, where it's normally used, and the traps that catch people when they convert text in bulk.

The cases, in one line each

• Sentence case: only the first word and proper nouns are capitalized. "How to plan a garden in spring"
• Title Case: major words are capitalized, while short articles, conjunctions and (depending on style) prepositions stay lowercase. "How to Plan a Garden in Spring"
• Capitalized Case: every word starts with a capital. "How To Plan A Garden In Spring"
• UPPER CASE: every letter is a capital. "HOW TO PLAN A GARDEN IN SPRING"
• lower case: no capitals at all. "how to plan a garden in spring"
• aLtErNaTiNg and InVeRsE: playful cases for memes and fixing accidental Caps Lock.
• Programming cases: camelCase, PascalCase, snake_case, SCREAMING_SNAKE_CASE, kebab-case, dot.case, plus URL slugs.

The most common mistake is treating Title Case and Capitalized Case as the same thing. They aren't, and editors notice.

Headlines and titles: Title Case, but pick a style

For article headlines, book and chapter titles, and formal page titles, Title Case is the usual choice in English. The trouble is that there isn't one Title Case. The major style guides agree on the basics. Capitalize the first and last word, capitalize nouns, verbs, adjectives and adverbs, and keep "a", "an", "the", "and", "or" and "but" lowercase in the middle. They disagree about prepositions.

Take the headline "walking through the park with the team after the storm":

• AP and APA: Walking Through the Park With the Team After the Storm
• Chicago and MLA: Walking through the Park with the Team after the Storm

AP and APA capitalize prepositions of four or more letters. Chicago and MLA keep prepositions lowercase however long they are. Neither is wrong. What matters is following whichever guide your publication, school or client uses, and sticking to it. I put together a fuller side-by-side, including how hyphenated words differ, in AP vs APA vs Chicago vs MLA title case.

A quick rule if no style is specified: news and web content usually follow AP, while books and general publishing usually follow Chicago.

Interfaces and documentation: sentence case

Most modern design systems use sentence case for buttons, menus, settings, form labels and headings in help docs. "Save changes", not "Save Changes". "Notification settings", not "Notification Settings". It reads like ordinary speech, it's easier to scan, and it removes the endless debate about whether "to" or "with" deserves a capital.

Whatever you choose, be consistent across one product. Mixing the two styles in a single menu is the most visible mistake.

Academic references: check the list separately

Academic styles often use different cases in different places. In APA, for example, your paper's own title and headings use title case, while article titles in the reference list use sentence case. So "Effects of Sleep on Memory" in the text becomes "Effects of sleep on memory" in the reference entry.

When you clean up capitalization in a paper, convert the reference list on its own pass. Don't run the whole document through one conversion and assume it's right.

Names and labels: Capitalized Case

Capitalized Case, where every word starts with a capital, works for personal names, place names, product names and short labels such as table column headings. It's the wrong choice for headlines, because it capitalizes words like "Of" and "The" that every major style keeps lowercase.

This is also exactly what spreadsheet and word-processor shortcuts produce. Excel's PROPER function and Word's "Capitalize Each Word" both give you "The Lord Of The Rings", not the correctly styled "The Lord of the Rings".

ALL CAPS: use sparingly

Capitals are fine for short labels, acronyms and the occasional emphasis. Whole sentences or paragraphs in capitals are harder to read, because word shapes disappear, and they come across as shouting in email and chat. If you've received a document typed in Caps Lock, converting it to sentence case is usually the fastest fix.

Code: follow the language's convention

In code, case isn't style. It's convention, and sometimes it's enforced by linters. The common patterns:

• camelCase: variables and functions in JavaScript, Java and similar languages. userName, getTotal
• PascalCase: classes, types and React components. UserProfile, OrderService
• snake_case: variables and functions in Python (PEP 8), and many database column names. user_name, created_at
• SCREAMING_SNAKE_CASE: constants and environment variables. MAX_RETRIES, API_BASE_URL
• kebab-case: CSS class names, file names and URL paths. main-header, user-settings
• dot.case: some config keys and namespaced identifiers. app.server.port

Converting between these by hand is error-prone, especially with acronyms (is it "userId" or "userID"?). That's a good job for a converter, followed by a quick review.

URLs: lowercase slugs with hyphens

For web addresses, the usual convention is lowercase words separated by hyphens, without punctuation or accents: /how-to-plan-a-garden. Hyphens are generally treated as word separators, mixed case can lead to duplicate URLs on some servers, and lowercase is simply easier to type and share. A slug generator turns a title into this format in one step.

Traps when converting in bulk

Automatic conversion is fast, but watch for these:

• Acronyms and brands. A naive converter turns NASA into "Nasa" and iPhone into "Iphone". Check the result, or use a tool that keeps known proper nouns.
• The pronoun "I". Lowercasing everything and then capitalizing sentence starts can leave a stray "i" in the middle of a sentence.
• Proper nouns in sentence case. No tool knows every name. Expect to fix some people, places and products by hand.
• Turkish and other languages. In Turkish, "i" uppercases to "İ" and "ı" to "I". Using English rules on Turkish text produces wrong letters, so use a converter that lets you choose the locale.
• IDs, emails and codes. Bulk Capitalized Case will happily change SKU-ab12 or an email address. Keep those out of the selection.

A tool for the job

I built Simple Case Converter because I kept running into these exact problems. You can choose the title style (AP, APA, Chicago or MLA), it restores the pronoun "I" in sentence case, it has a smart proper-noun option and a locale setting for English, Turkish and German, and it covers the programming cases and slugs. The text is processed in your browser, so nothing you paste is uploaded. Whatever tool you use, the steps are the same: pick the case for the context, convert, then read the result once before you publish.

Ankur Bhardwaj