How to Use strtoupper in PHP: Convert Strings to Uppercase

Use the strtoupper function in PHP to convert all letters in a string to uppercase. Pass the string as an argument like strtoupper('hello'), which returns 'HELLO'.

Syntax

The strtoupper function takes one string argument and returns a new string with all alphabetic characters converted to uppercase.

• string: The input string you want to convert.
• Returns: A string with all letters in uppercase.

php

string strtoupper(string $string)

Example

This example shows how to convert a lowercase string to uppercase using strtoupper.

php

<?php
$input = 'hello world';
$output = strtoupper($input);
echo $output;
?>

Output

HELLO WORLD

Common Pitfalls

One common mistake is forgetting that strtoupper does not change the original string but returns a new one. Also, it only affects alphabetic characters and leaves numbers and symbols unchanged.

Another pitfall is passing non-string types without converting them first, which can cause warnings.

php

<?php
// Wrong: expecting original string to change
$word = 'hello';
strtoupper($word);
echo $word; // outputs 'hello', not uppercase

// Right: assign the result
$word = 'hello';
$word = strtoupper($word);
echo $word; // outputs 'HELLO'
?>

Output

hello
HELLO

Quick Reference

Function	Description	Example	Output
strtoupper	Converts string to uppercase	strtoupper('php')	'PHP'
strtolower	Converts string to lowercase	strtolower('PHP')	'php'
ucfirst	Capitalizes first letter	ucfirst('php')	'Php'

Key Takeaways

Use strtoupper to convert all letters in a string to uppercase in PHP.

strtoupper returns a new string; it does not modify the original variable.

Only alphabetic characters are changed; numbers and symbols stay the same.

Always assign the result of strtoupper to a variable if you want to keep the uppercase string.