Convert String to Uppercase in PHP

In PHP, converting a string to uppercase is a straightforward task thanks to built-in functions designed for handling both standard ASCII and multibyte Unicode characters. This article explains how to use strtoupper() for basic English strings and mb_strtoupper() for multi-byte character sets like UTF-8, complete with practical code examples.

Using strtoupper() for Standard Strings

The simplest way to convert a string to uppercase in PHP is by using the strtoupper() function. This function takes a string as its argument and returns the string with all alphabetic characters converted to uppercase.

<?php
$lowercaseString = "hello world!";
$uppercaseString = strtoupper($lowercaseString);

echo $uppercaseString; // Outputs: HELLO WORLD!
?>

Note: strtoupper() is locale-dependent and only works reliably with standard ASCII characters. It will not correctly convert accented characters or non-Latin alphabets.

Using mb_strtoupper() for Multibyte (UTF-8) Strings

If your application handles international characters, accents, or non-Latin scripts (such as Spanish, Cyrillic, or German), you should use mb_strtoupper(). This multibyte-safe function ensures that characters like “é” or “ñ” are capitalized correctly.

<?php
$multibyteString = "café";

// Standard strtoupper() fails on "é"
echo strtoupper($multibyteString); // Outputs: CAFé (or broken characters)

// mb_strtoupper() handles it correctly
echo mb_strtoupper($multibyteString, 'UTF-8'); // Outputs: CAFÉ
?>

Key Differences Summary