How to create Temperature converter using JavaScript


Temperature conversion is a fundamental concept that finds applications in various fields, from meteorology to cooking. In this detailed guide, we create temperature converter using JavaScript. Whether you’re a beginner or an experienced developer this guide is for you. By the end, you’ll have mastered the art of temperature conversion and built a versatile temperature converter tool using JavaScript.

Understanding Celsius and Fahrenheit

Before we begin, let’s take a moment to understand the Celsius and Fahrenheit temperature scales. Celsius (°C) is the standard unit of temperature measurement in most countries, while Fahrenheit (°F) is commonly used in the United States. To convert between these scales:

  • Celsius to Fahrenheit: Multiply the Celsius temperature by 9/5 and add 32.
  • Fahrenheit to Celsius: Subtract 32 from the Fahrenheit temperature and then multiply by 5/9.

Building the Temperature Converter

Now, We’ll create a user-friendly web page where users can input temperatures in Celsius or Fahrenheit, and instantly see the converted values.

  <title>Temperature Converter</title>
  <h2>Temperature Converter</h2>
  <label for="temperature">Enter Temperature:</label>
  <input type="number" id="temperatureInput">
  <select id="unitSelect">
    <option value="celsius">Celsius</option>
    <option value="fahrenheit">Fahrenheit</option>
  <button onclick="convertTemperature()">Convert</button>
  <p id="result"></p>

    // Function to convert Celsius to Fahrenheit
    function celsiusToFahrenheit(celsius) {
      return celsius * 9 / 5 + 32;

    // Function to convert Fahrenheit to Celsius
    function fahrenheitToCelsius(fahrenheit) {
      return (fahrenheit - 32) * 5 / 9;

    // Function to handle button click and perform conversion
    function convertTemperature() {
      // Get the temperature entered by the user
      const temperatureInput = parseFloat(document.getElementById('temperatureInput').value);
      // Get the selected unit
      const selectedUnit = document.getElementById('unitSelect').value;
      // Perform conversion based on the selected unit
      let result;
      if (selectedUnit === 'celsius') {
        result = `${temperatureInput}°C is equal to ${celsiusToFahrenheit(temperatureInput)}°F`;
      } else {
        result = `${temperatureInput}°F is equal to ${fahrenheitToCelsius(temperatureInput)}°C`;

      // Display the result on the page
      document.getElementById('result').innerText = result;

Explanation of the Code

In the HTML code snippet above, we create a simple web page with an input field for the user to enter the temperature and a dropdown to select the unit (Celsius or Fahrenheit). When the user clicks the “Convert” button, the convertTemperature() function is called.

  • The celsiusToFahrenheit() function converts Celsius to Fahrenheit.
  • The fahrenheitToCelsius() function converts Fahrenheit to Celsius.
  • The convertTemperature() function gets the temperature and selected unit entered by the user, performs the conversion based on the selected unit, and displays the result on the page.


Let’s illustrate how our temperature converter works with a practical example. Suppose you want to convert 20 degrees Celsius to Fahrenheit. Simply enter “20” in the input box, select “Celsius” from the dropdown, click the button, and you’ll see the result displayed on the page: 20°C is equal to 68°F. You can also convert from Fahrenheit to Celsius by selecting “Fahrenheit” from the dropdown.


In this comprehensive guide, we’ve created temperature converter using JavaScript. From understanding the Celsius and Fahrenheit scales to building a functional temperature converter tool capable of handling both conversions, you’ve gained valuable insights and practical coding experience. Armed with this knowledge, you’re well-equipped to tackle temperature-related challenges in your future projects.

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