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, divide by 5, then add 32. This formula changes the scale from Celsius to Fahrenheit, which have different zero points and increments.

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(celsius + " Celsius is " + fahrenheit + " Fahrenheit");
    }
}

Output

25.0 Celsius is 77.0 Fahrenheit

Dry Run

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

1

Input Celsius

celsius = 25

2

Multiply by 9

25 * 9.0 = 225.0

3

Divide by 5

225.0 / 5.0 = 45.0

4

Add 32

45.0 + 32 = 77.0

5

Output Fahrenheit

fahrenheit = 77.0

Step	Operation	Result
1	Input Celsius	25
2	Multiply by 9	225.0
3	Divide by 5	45.0
4	Add 32	77.0
5	Output Fahrenheit	77.0

Why This Works

Step 1: Multiply Celsius by 9/5

The formula fahrenheit = (celsius * 9/5) + 32 converts the scale size from Celsius to Fahrenheit by multiplying by 9/5.

Step 2: Add 32 to adjust zero point

Adding 32 shifts the zero point from Celsius to Fahrenheit, because 0°C equals 32°F.

Alternative Approaches

Using integer arithmetic

java

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

This uses integer math which can lose decimal precision but is simpler for whole numbers.

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) {
        double celsius = 25;
        System.out.println(celsius + " Celsius is " + convert(celsius) + " Fahrenheit");
    }
}

Separates conversion logic into a reusable method for cleaner code.

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 space usage is constant.

Which Approach is Fastest?

All approaches run in constant time; using integer arithmetic is slightly faster but less precise.

Approach	Time	Space	Best For
Double arithmetic	O(1)	O(1)	Accurate decimal conversion
Integer arithmetic	O(1)	O(1)	Simple whole number conversion
Method-based conversion	O(1)	O(1)	Reusable and clean code