PHP How to Convert String to Uppercase Easily

Use the built-in PHP function strtoupper() to convert any string to uppercase, like strtoupper('hello') which returns 'HELLO'.

Examples

Inputhello

OutputHELLO

InputPhp is fun!

OutputPHP IS FUN!

Input123abc!@#

Output123ABC!@#

How to Think About It

To convert a string to uppercase in PHP, think of changing every letter to its capital form. PHP provides a simple function that takes your string and returns a new string with all letters in uppercase, leaving numbers and symbols unchanged.

Algorithm

1

Get the input string.

2

Pass the string to the uppercase conversion function.

3

Receive the converted uppercase string.

4

Return or print the uppercase string.

Code

php

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

Output

HELLO WORLD!

Dry Run

Let's trace converting 'hello' to uppercase using strtoupper()

1

Input string

The input string is 'hello'

2

Call strtoupper()

strtoupper('hello') processes each character

3

Output string

Returns 'HELLO'

Original	Uppercase
hello	HELLO

Why This Works

Step 1: Function Purpose

The strtoupper() function converts all alphabetic characters in the string to uppercase.

Step 2: Non-alphabetic Characters

Characters like numbers and symbols remain unchanged because they have no uppercase form.

Step 3: Return Value

The function returns a new string with uppercase letters, leaving the original string unchanged.

Alternative Approaches

mb_strtoupper() for multibyte strings

php

<?php
$input = "héllo wörld!";
$output = mb_strtoupper($input, 'UTF-8');
echo $output;
?>

Use this when working with UTF-8 strings containing accented or special characters to correctly convert them.

Manual loop with strtoupper() on each character

php

<?php
$input = "hello";
$output = '';
for ($i = 0; $i < strlen($input); $i++) {
    $output .= strtoupper($input[$i]);
}
echo $output;
?>

This is less efficient and more complex but shows how uppercase conversion works character by character.

Complexity: O(n) time, O(n) space

Time Complexity

The function processes each character once, so time grows linearly with string length.

Space Complexity

A new string is created for the uppercase result, so space also grows linearly with input size.

Which Approach is Fastest?

strtoupper() is fastest for ASCII strings; mb_strtoupper() is needed for UTF-8 but slightly slower due to encoding handling.

Approach	Time	Space	Best For
strtoupper()	O(n)	O(n)	Simple ASCII strings
mb_strtoupper()	O(n)	O(n)	UTF-8 strings with accents
Manual loop with strtoupper()	O(n)	O(n)	Educational purposes, not recommended