Sentence Case Converter

Text Tools Case and Formatting

Sentence case capitalises only the first word of each sentence, the pronoun I and proper nouns. Paste text and the converter lowercases the rest, starting a new sentence after a full stop, question mark, exclamation mark or line break. For example, HOW NASA TESTS A CABLE becomes How NASA tests a cable when acronyms are kept.

About this tool

Headings copied from a slide deck, notes typed with caps lock on and product names written in Title Case all need the same fix before they go into an article, an APA reference list or a UI label: sentence case. This converter lowercases each word, then raises the first letter of every sentence and the pronoun I. Words typed entirely in capitals, such as NASA or USB, can be left alone with the acronym switch, and a count shows how many were kept and how many letters changed. The limit is proper nouns written in normal case: the converter cannot tell that paris or monday should be capitalised, so names of people, places and brands need a quick read-through afterwards.

How to use it

Paste or open text
Type in the box, paste from anywhere, or open a .txt file from your device.
Choose acronym handling
Leave the switch on to keep all-capital words like USB, or turn it off when the whole text was typed in caps lock.
Set the pronoun rule
Keep the checkbox ticked so i, i'm and i'll become I, I'm and I'll.
Copy the result
Use Copy result and check proper nouns before pasting it back.

Examples

Shouted caps, two sentences

Text to convert: THE QUICK BROWN FOX. IT JUMPED OVER THE DOG!
Keep acronyms in capitals (NASA, USB): No
Capitalise the pronoun I: Yes

Result Sentence case: The quick brown fox. It jumped over the dog!
Sentences: 2
Words: 9
Letters changed: 32
Acronyms kept: 0

Lowercased every word.
Capitalised the first letter of 2 sentences (after . ! ? or a new line).
32 characters changed case.

With acronyms off, every word is lowercased and only the first letter after each full stop or exclamation mark goes back up.

A Title Case heading with acronyms

Text to convert: How NASA Tests A New USB Cable
Keep acronyms in capitals (NASA, USB): Yes
Capitalise the pronoun I: Yes

Result Sentence case: How NASA tests a new USB cable
Sentences: 1
Words: 7
Letters changed: 4
Acronyms kept: 2

Lowercased every word except 2 all-capital acronyms.
Capitalised the first letter of 1 sentence (after . ! ? or a new line).
4 characters changed case.

NASA and USB stay in capitals because they were typed in capitals; the other words drop to lowercase.

Lowercase notes on two lines

Text to convert: yesterday i'm sure i saw it then i left
Keep acronyms in capitals (NASA, USB): Yes
Capitalise the pronoun I: Yes

Result Sentence case: Yesterday I'm sure I saw it
Then I left
Sentences: 2
Words: 9
Letters changed: 5
Acronyms kept: 0

Lowercased every word except 0 all-capital acronyms.
Capitalised the first letter of 2 sentences (after . ! ? or a new line).
5 characters changed case.

Each new line starts a sentence, and every standalone i, including i'm, becomes I.

How it is calculated

output = lowercase(words) with first letter raised after . ! ? or a line break

sentence start: the first letter of the text, of each line, and after a word ending in . ! or ?
acronym: a word of two or more letters typed entirely in capitals

The text is split at whitespace. Each word is lowercased unless it is an acronym and the switch is on. The first letter found after a sentence start is capitalised, so a leading quote mark or bracket does not block it. Standalone i and its contractions become I when the checkbox is ticked. Line breaks and spacing are kept exactly as typed.

When not to use it

Text full of proper nouns in ordinary case, such as names and cities, will lose their capitals.
Abbreviations like e.g. or Dr. end in a full stop, so the next word gets capitalised by mistake.

Common mistakes

Leaving acronyms on for text typed in caps lock, which keeps every word in capitals.
Using sentence case for a book title when the style guide asks for title case.

Frequently asked questions

What is the difference between sentence case and title case?

Sentence case capitalises only the first word and proper nouns, as in a normal sentence. Title case capitalises most words, leaving articles and short prepositions lowercase. APA uses sentence case for article titles in reference lists and title case for headings.

Why did my acronyms stay in capitals?

With the acronym switch on, any word of two or more letters typed fully in capitals is left as it is. Turn the switch off when the source was typed with caps lock and you want everything lowercased first.

Does it capitalise names of people and places?

No. It has no dictionary of proper nouns, so a name written as london stays lowercase unless it starts a sentence. Names already typed in capitals are kept only when the acronym switch is on and they are all capitals.

How does it decide where a sentence starts?

At the start of the text, at every line break, and after a word that ends in a full stop, question mark or exclamation mark, including one followed by a closing quote or bracket.

Is my text sent to a server?

No. The conversion runs in your browser, and an opened file is read locally on your device without being uploaded.

Cite this tool

Using this tool in an assignment, article or report? Copy a citation, or a link for your website.

APA

Tools Directory Editorial Team. (2026, October 26). Sentence Case Converter. Tools Directory. Retrieved October 28, 2026, from https://tools.milunir.com/text-tools/case-and-formatting/sentence-case-converter/

MLA

Tools Directory Editorial Team. “Sentence Case Converter.” Tools Directory, 26 Oct. 2026, https://tools.milunir.com/text-tools/case-and-formatting/sentence-case-converter/. Accessed 28 Oct. 2026.

Chicago

Tools Directory Editorial Team. “Sentence Case Converter.” Tools Directory. Last modified October 26, 2026. Accessed October 28, 2026. https://tools.milunir.com/text-tools/case-and-formatting/sentence-case-converter/.

Link

<a href="https://tools.milunir.com/text-tools/case-and-formatting/sentence-case-converter/">Sentence Case Converter – Tools Directory</a>