Java Program to Convert Celsius to Fahrenheit

To convert Celsius to Fahrenheit in Java, use the formula fahrenheit = (celsius * 9 / 5) + 32. For example, double fahrenheit = (celsius * 9.0 / 5.0) + 32; converts a Celsius value to Fahrenheit.

Examples

Input0

Output32.0

Input25

Output77.0

Input-40

Output-40.0

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, which uses a different zero point and unit size.

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

java

public class CelsiusToFahrenheit {
    public static void main(String[] args) {
        double celsius = 25;
        double fahrenheit = (celsius * 9.0 / 5.0) + 32;
        System.out.println("Fahrenheit: " + fahrenheit);
    }
}

Output

Fahrenheit: 77.0

Dry Run

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

1

Start with Celsius value

celsius = 25

2

Multiply by 9 and divide by 5

(25 * 9) / 5 = 225 / 5 = 45

3

Add 32 to get Fahrenheit

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

The Celsius temperature is multiplied by 9 to scale it according to the Fahrenheit unit size.

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 the freezing point of water.

Alternative Approaches

Using a method to convert

java

public class CelsiusToFahrenheit {
    public static double convert(double celsius) {
        return (celsius * 9.0 / 5.0) + 32;
    }
    public static void main(String[] args) {
        System.out.println("Fahrenheit: " + convert(25));
    }
}

This approach improves code reuse by putting the conversion in a method.

Using integer arithmetic (less precise)

java

public class CelsiusToFahrenheit {
    public static void main(String[] args) {
        int celsius = 25;
        int fahrenheit = (celsius * 9 / 5) + 32;
        System.out.println("Fahrenheit: " + fahrenheit);
    }
}

This uses integers only but loses decimal precision.

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 run in constant time; using a method adds slight overhead but improves code clarity.

Approach	Time	Space	Best For
Direct formula	O(1)	O(1)	Simple quick conversion
Method encapsulation	O(1)	O(1)	Reusable and clean code
Integer arithmetic	O(1)	O(1)	When decimals are not needed