JavaScript Program to Convert Celsius to Fahrenheit

Use the formula fahrenheit = (celsius * 9/5) + 32 in JavaScript like const fahrenheit = (celsius * 9/5) + 32; to convert Celsius to Fahrenheit.

Examples

Input0

Output32

Input25

Output77

Input-40

Output-40

How to Think About It

To convert Celsius to Fahrenheit, multiply the Celsius value by 9, then divide by 5, and finally add 32. This formula changes the temperature scale from Celsius to Fahrenheit.

Algorithm

1

Get the temperature value in Celsius.

2

Multiply the Celsius value by 9.

3

Divide the result by 5.

4

Add 32 to the result.

5

Return the final value as Fahrenheit.

Code

javascript

function celsiusToFahrenheit(celsius) {
  const fahrenheit = (celsius * 9 / 5) + 32;
  return fahrenheit;
}

console.log(celsiusToFahrenheit(0));
console.log(celsiusToFahrenheit(25));
console.log(celsiusToFahrenheit(-40));

Output

32
77
-40

Dry Run

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

1

Input Celsius

celsius = 25

2

Multiply by 9

25 * 9 = 225

3

Divide by 5

225 / 5 = 45

4

Add 32

45 + 32 = 77

5

Return Fahrenheit

fahrenheit = 77

Step	Operation	Result
1	Input Celsius	25
2	Multiply by 9	225
3	Divide by 5	45
4	Add 32	77
5	Return Fahrenheit	77

Why This Works

Step 1: Multiply Celsius by 9

Multiplying by 9 scales the Celsius temperature to the Fahrenheit scale proportionally.

Step 2: Divide by 5

Dividing by 5 adjusts the scale difference between Celsius and Fahrenheit degrees.

Step 3: Add 32

Adding 32 shifts the zero point from Celsius to Fahrenheit, aligning freezing points.

Alternative Approaches

Arrow function

javascript

const celsiusToFahrenheit = celsius => (celsius * 9 / 5) + 32;
console.log(celsiusToFahrenheit(100));

Shorter syntax using arrow function, good for concise code.

Using Math.round for integer output

javascript

function celsiusToFahrenheit(celsius) {
  return Math.round((celsius * 9 / 5) + 32);
}
console.log(celsiusToFahrenheit(36.6));

Rounds the result to nearest integer, useful when decimals are not needed.

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

Time Complexity

The calculation uses 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 constant-time calculation; differences are mainly in syntax and readability.

Approach	Time	Space	Best For
Standard function	O(1)	O(1)	Clear and easy to understand
Arrow function	O(1)	O(1)	Concise syntax for simple functions
Rounded output	O(1)	O(1)	When integer results are preferred