PHP How to Convert Celsius to Fahrenheit with Example

To convert Celsius to Fahrenheit in PHP, use the formula F = (C * 9/5) + 32 where C is the Celsius value; for example, $fahrenheit = ($celsius * 9 / 5) + 32;.

Examples

Input0

Output32

Input25

Output77

Input-40

Output-40

How to Think About It

To convert Celsius to Fahrenheit, multiply the Celsius temperature by 9, then divide by 5, and finally add 32. This formula changes the scale from Celsius to Fahrenheit by adjusting for the different zero points and unit sizes.

Algorithm

1

Get the Celsius temperature input.

2

Multiply the Celsius value by 9.

3

Divide the result by 5.

4

Add 32 to the result.

5

Return or print the Fahrenheit temperature.

Code

php

<?php
$celsius = 25;
$fahrenheit = ($celsius * 9 / 5) + 32;
echo "Temperature in Fahrenheit: " . $fahrenheit;
?>

Output

Temperature in Fahrenheit: 77

Dry Run

Let's trace converting 25 Celsius to Fahrenheit through the code

1

Input Celsius

Celsius value is 25

2

Multiply by 9

25 * 9 = 225

3

Divide by 5

225 / 5 = 45

4

Add 32

45 + 32 = 77

Step	Calculation	Result
Multiply by 9	25 * 9	225
Divide by 5	225 / 5	45
Add 32	45 + 32	77

Why This Works

Step 1: Multiply Celsius by 9

This scales the Celsius value to match the Fahrenheit scale's unit size.

Step 2: Divide by 5

Dividing by 5 adjusts the scale ratio between Celsius and Fahrenheit.

Step 3: Add 32

Adding 32 shifts the zero point from Celsius to Fahrenheit.

Alternative Approaches

Using a function

php

<?php
function celsiusToFahrenheit(float $celsius): float {
    return ($celsius * 9 / 5) + 32;
}

echo celsiusToFahrenheit(25);

Encapsulates conversion in a reusable function for cleaner code.

Using round for integer output

php

<?php
$celsius = 25;
$fahrenheit = round(($celsius * 9 / 5) + 32);
echo $fahrenheit;

Rounds the result to nearest whole number for simpler display.

Complexity: O(1) time, O(1) space

Time Complexity

The calculation involves a fixed number of arithmetic operations, so it runs in constant time.

Space Complexity

Only a few variables are used, so the space needed is constant.

Which Approach is Fastest?

All approaches perform the same simple calculation, so they have identical performance; using a function improves code reuse but does not affect speed.

Approach	Time	Space	Best For
Direct formula	O(1)	O(1)	Quick one-off conversions
Function encapsulation	O(1)	O(1)	Reusable and clean code
Rounded output	O(1)	O(1)	User-friendly integer results