Case Converter (Upper, Lower, Title, Sentence)

What this tool does

Formatting rules differ between systems: some databases are case-sensitive, some forms demand capitals, and headings need title case. Retyping text to change its case is error-prone and slow, especially in a spreadsheet. This tool converts it instantly and, more usefully, tells you the function to use if the text lives in a column rather than on a page.

Method

The conversion is driven by Unicode character properties rather than an ASCII table, so it works for accented Latin letters and for other cased scripts. Title Case capitalises the first letter of each word and lowercases the remainder; Sentence case lowercases everything and then capitalises the first letter after a full stop, question mark or exclamation mark. An optional cleanup collapses runs of spaces and blank lines, which is the usual companion fix when data has been pasted from a PDF.

Example

Mode	Result	Spreadsheet
UPPER CASE	TIENG VIET	=UPPER(A1)
lower case	tieng viet	=LOWER(A1)
Title Case	Tieng Viet	=PROPER(A1)
Sentence case	Tieng viet	=UPPER(LEFT(A1,1))&LOWER(MID(A1,2,LEN(A1)))

Title case is not "capitalise every word"

The four modes look mechanical, but title case has judgement in it. A newspaper headline capitalises the first and last word and every word except short grammatical ones — articles (a, an, the), coordinating conjunctions (and, but, or) and short prepositions (of, in, on, to). A filename or a form label usually wants every significant word capitalised.

Style	Result	Rule
Headline (AP)	The Lord of the Rings	“of” and “the” lowercase mid-title
Every word	The Lord Of The Rings	Simplest and most common in software
Sentence case	The lord of the rings	Only the first word

This tool implements the simple every-word form, which is predictable and is what most form fields and filenames expect. It will not match a publication's house style — that needs a word list, and different style guides disagree on which words are “short” (is “about” capitalised? AP says yes, some guides say no).

Sentence case preserves proper nouns

Lowercasing everything after the first letter destroys names: “I visited London with Mary” becomes “I visited london with mary”. There is no algorithm that can know “London” is a proper noun without a dictionary or a language model, so a mechanical sentence-case converter has to either accept the lowercasing or leave the rest of the string untouched.

This is why sentence case is the mode that most often needs a manual pass. Use it when the input is already uniformly cased — a shouted sentence, an ALL CAPS field — and not when it contains names you need to keep.

Locales where uppercase changes length

Case mapping is not always one-to-one, and the exceptions surprise people:

Character	Uppercase	What happens
ß	SS	One character becomes two
i (Turkish)	İ	Dotted capital, not I — locale-specific
fi (ligature)	FI	Compatibility decomposition before uppercasing
ǰ	J̌	Base plus combining mark

The Turkish i is the one that causes real bugs: "istanbul".toUpperCase() gives “ISTANBUL” in most locales but should give “İSTANBUL” in Turkish. A case converter that ignores the locale silently produces the wrong word for Turkish users. This tool applies standard Unicode case mapping, which is the right choice for code identifiers and URLs, but is not locale-aware.

What "collapse extra spaces" does

The cleanup option runs after the case conversion and collapses runs of spaces and blank lines into a single space or a single line break. It is aimed at text pasted from a PDF or a web page, where every visual line ends with hard-wrapped whitespace and the result reads as ragged.

It is deliberately opt-in rather than automatic: collapsing whitespace in code, in a fixed-width layout, or in Markdown where indentation is meaningful would change the document's structure. If your input is prose, turn it on; if it is code or markup, leave it off.

Case is not the same as collation

Converting case does not change how text sorts. Two strings that differ only in case compare unequal under a byte comparison but equal under a case-insensitive collator. If you are deduplicating a list, compare with a case-insensitive collator rather than converting case first — converting destroys the original and can merge values that were intentionally distinct.

Where each mode belongs

• UPPER — constants, codes, acronyms, emphasis. Not for prose.
• lower — identifiers, emails, slugs, file extensions.
• Title — headings, labels, filenames. Decide your rule for short words.
• Sentence — prose that was typed in caps, or a first-pass normalisation.

One caution for identifiers: case conversion is not a substitute for a proper slug or a validated identifier. Uppercasing a value that will be used as a key can create collisions between values that differed only in case, and there is no way to recover the original afterwards.

Frequently asked questions

Go deeper

Longer explanations of the problems this tool solves:

Cleaning text that looks right and behaves wrong

Sources

• Unicode Standard, character case properties (uppercase, lowercase, titlecase mappings).
• Google Sheets and Microsoft Excel text function documentation for UPPER, LOWER and PROPER.