Title Case vs Sentence Case: Which Should You Use?

The two styles

Sentence case capitalises only the first word and any proper nouns: How to reduce image file size.

Title case capitalises the significant words: How to Reduce Image File Size. Both are correct. Which one you use is a house style decision, and the only real error is switching between them at random within the same document or interface.

What title case actually capitalises

The convention is to capitalise nouns, verbs, adjectives, adverbs and pronouns, and to leave articles, coordinating conjunctions and short prepositions in lower case — unless they are the first or last word, which are always capitalised.

The details vary by style guide. Chicago lower-cases all prepositions regardless of length; AP capitalises those of four letters or more, which is why you see both Sign in to Your Account and Sign In To Your Account in the wild. Pick a guide and follow it rather than deciding word by word.

Why sentence case is winning in product writing

The major design systems from Google, Apple, Microsoft and others have converged on sentence case for interface text. It reads faster, because capital letters function as signals and a line full of them carries no signal at all. It is less shouty in an interface where almost every element has a label.

It is also markedly easier to get right in a team, and dramatically easier to translate. Many languages have their own capitalisation rules — German capitalises all nouns, French and Spanish capitalise far less than English — and title case simply does not survive translation.

Where title case still belongs

Book, film and article titles in most editorial style guides. Formal headlines in publications that use it. Proper names of products and features. Legal document headings. If your organisation has an established editorial voice built on title case, consistency with it is worth more than following a trend.

Two things to avoid

All caps for anything longer than a couple of words. It slows reading measurably by removing the word shapes readers rely on, and some screen readers interpret capitalised strings as acronyms and spell them out letter by letter.

Faking case with CSS. Applying a text transform changes the appearance but not the underlying text, so what gets copied, searched, read aloud or exported is the original. If a heading should be in sentence case, write it in sentence case.

Converting between them

Automatic conversion handles the mechanical part well and cannot know your exceptions. Proper nouns, acronyms such as PDF, API and HTML, brand names with deliberate capitalisation, and words like iPhone all need a human pass afterwards. Convert first, then read the result — the errors are always in the same few places.