Sentence Case vs Title Case: Which to Use, and What Automatic Conversion Gets Wrong
What four style guides say, why some teams standardize on sentence case, and what happens to PDF, iMessage and other spellings when text is converted automatically.
Is it "How to Write a Cover Letter" or "How to write a cover letter"? Both are correct, and which one you pick matters less than picking one and applying it everywhere. This post compares what four sources say about sentence case and title case, why some teams have moved to sentence case, and what goes wrong when a tool converts headings for you. For the rules of title case itself, see Title Case Rules Explained.
Need to switch a heading? The case converter has Sentence case and Title Case options and runs in your browser, with no upload.
What Four Sources Say
| Source | Guidance |
|---|---|
| Microsoft Writing Style Guide | "Use sentence-style capitalization in most titles and headings." Blog post titles use it too, and the first word after a colon is capitalized. |
| Google developer documentation style guide | "In document titles and headings, use sentence case." The first word after a colon is lowercase, with exceptions such as proper nouns and labels like Note. |
| APA Style | Sentence case for titles in reference list entries, rather than the title case printed on the works themselves. |
| USAGov | In 2023 it switched all content on its new English beta website to sentence case. |
Notice the disagreement in the first two rows: Microsoft capitalizes the word after a colon and Google does not. That matters, because 112 of the 228 titles on this blog, 49%, contain a colon.
Why Teams Move to Sentence Case
USAGov published its reasoning. About 80% of the federal websites it reviewed used title case, but several agencies had adopted sentence case in 2022 and 2023 redesigns, and the team said it was easier for content designers to apply consistently. Page titles and headings were also getting longer, and moving to sentence case reduced wrapping on small screens in some cases. Surveys after the switch showed no change in trustworthiness ratings.
The evidence does not crown a winner. USAGov found mixed opinions on readability and no definitive answer on accessibility: title case looks larger, which helps some low-vision readers, while sentence case can be easier to skim. The practical argument is consistency.
What Automatic Conversion Gets Wrong
Going from sentence case to title case only has to decide which words are major. Going the other way has to decide which capitals are names, and a simple program cannot tell. I tested the simplest approach, lowercase everything and capitalize the first letter, on the 228 titles of this blog. In 89 of them (39%), at least one acronym or brand spelling would be damaged. Examples:
- How to Compare Two PDF Documents… becomes How to compare two pdf documents…
- iMessage vs. SMS becomes Imessage vs. sms
- SynthID and AI Watermarking… becomes Synthid and ai watermarking…
The 39% counts only words with several capitals, such as PDF, AI or LinkedIn. Names with a single capital, like Google or Discord, can't be detected this way, so the real number is higher. No converter can know every name, so the output always needs a read.
Update: until recently, this site's own case converter did exactly this to acronyms: PDF became Pdf or pdf. Its Title Case and Sentence case buttons now keep words with a capital inside, such as PDF or iPhone, as typed, and Title Case leaves short words like of and the lowercase. Names with a single capital, such as Google, are still lowercased by the Sentence case button, so the read-through above still applies.
A Short Checklist
- Pick one style per content type and write it down: headings, page titles, buttons.
- Decide the colon rule. Follow Microsoft or Google, and stick to it.
- After converting, check: acronyms (PDF, SEO), brand spellings (iPhone, LinkedIn), the word "I", people and place names, and the word after a colon.
- Leave reference titles to your citation style. APA, for example, has its own rule for them.
For a related conversion task, see How to Convert Text to Uppercase or Lowercase.
The honest summary: Microsoft, Google and USAGov favor sentence case for headings, APA uses it for reference titles, and the research does not settle which style reads better. Choose one, set a colon rule, and read every converted heading, because roughly four in ten of my own titles contained something an automatic lowercase would break.
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