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JavaScript: Convert Degrees to Radians


In trigonometry, angles are often measured in degrees. However, many trigonometric functions in JavaScript, such as Math.sin() and Math.cos(), require angles to be in radians. Therefore, it is important to know how to convert angles from degrees to radians in order to perform accurate calculations in JavaScript.

Converting degrees to radians allows us to work with angles in a format that is compatible with the trigonometric functions provided by JavaScript's Math library. By making this conversion, we can easily compute the sine, cosine, and other trigonometric values of an angle using built-in JavaScript functions.

Converting degrees to radians is a fundamental concept in trigonometry and is essential for a wide range of applications, including geometry, physics, and computer graphics. Understanding how to perform this conversion is crucial for anyone working with JavaScript in these fields.

Understanding Degrees and Radians

In trigonometry, angles can be measured in two different units: degrees and radians.

Degrees are the more commonly used unit of measurement for angles. A circle is divided into 360 equal parts, with each part representing one degree. This makes degrees a convenient unit for everyday use and simple calculations.

Radians, on the other hand, are a unit of measurement that is closely related to the properties of circles. In a circle, there are 2π (approximately 6.28) radians, which corresponds to the circumference of the circle. Radians are often used in more advanced mathematical calculations, particularly in trigonometry and calculus, due to their mathematical properties that simplify complex formulas.

The main difference between degrees and radians is the scale of measurement. While degrees divide a circle into 360 equal parts, radians divide a circle into 2π parts. This means that a full circle in degrees is equal to 360 degrees, but in radians, it is equal to 2π radians.

To illustrate this difference, let's consider a few examples:

  • An angle of 90 degrees is approximately equal to π/2 radians.
  • An angle of 180 degrees is equal to π radians.
  • An angle of 270 degrees is approximately equal to 3π/2 radians.
  • An angle of 360 degrees is equal to 2π radians.

Understanding the difference between degrees and radians is important for performing accurate trigonometric calculations and for working with mathematical formulas that require angles to be in radians.

Mathematical Formulas for Conversion

In order to convert degrees to radians, we can use the following formula:

radians = degrees * (π / 180)

Let's break down the formula and explain each part:

  • degrees: This represents the angle measurement in degrees that we want to convert to radians.

  • π (pi): This is a mathematical constant that represents the ratio of a circle's circumference to its diameter. In JavaScript, we can access the value of pi using Math.PI.

  • 180: This is the total number of degrees in a circle. Since there are 360 degrees in a circle, dividing it by 2 gives us 180 degrees.

To illustrate the conversion process, let's use an example. Let's say we want to convert an angle of 45 degrees to radians. We can plug in the values into the formula:

radians = 45 * (π / 180)

To calculate the value of radians, we need to substitute the value of pi and perform the calculation:

radians = 45 * (3.14159 / 180)

Simplifying the calculation further:

radians = 0.78539

Therefore, an angle of 45 degrees is equivalent to approximately 0.78539 radians.

By using this formula, we can easily convert any angle from degrees to radians in JavaScript.

JavaScript Functions for Conversion

In JavaScript, there are built-in functions available in the Math library that allow you to easily convert degrees to radians. The Math library provides a variety of mathematical functions and constants.

One of the functions provided by the Math library is the Math.radians() function, which specifically converts degrees to radians. This function takes an angle in degrees as input and returns the equivalent angle in radians.

Here is an example of how to use the Math.radians() function:

const degrees = 45;
const radians = Math.radians(degrees);
console.log(radians); // Output: 0.7853981633974483

In the code snippet above, we have a variable degrees which holds the angle in degrees that we want to convert. We then use the Math.radians() function to convert the degrees value to radians and store the result in the radians variable. Finally, we log the radians value to the console.

The Math.radians() function simplifies the process of converting degrees to radians by handling the conversion internally. It follows the mathematical formula radians = degrees * (Math.PI / 180), where Math.PI represents the value of pi and 180 is the number of degrees in a full circle.

Using the Math.radians() function is convenient and efficient, as it eliminates the need to manually perform the conversion calculation.

Custom Conversion Function

In JavaScript, you can also write a custom function to convert degrees to radians. This can be useful when you want more control over the conversion process or when you're working on a project that doesn't have access to the Math library.

To create a custom conversion function, you can use the following formula:

function degreesToRadians(degrees) {
  var radians = degrees * (Math.PI / 180);
  return radians;

Here's how the custom function works:

  1. The function degreesToRadians takes a parameter degrees, which represents the angle in degrees that you want to convert to radians.
  2. Inside the function, the angle in degrees is multiplied by (Math.PI / 180). This converts the angle to radians using the formula radians = degrees * (Math.PI / 180).
  3. The result, radians, is then returned by the function.

You can use this custom function like any other JavaScript function. Here's an example:

var angleInDegrees = 45;
var angleInRadians = degreesToRadians(angleInDegrees);
console.log(angleInRadians); // Output: 0.7853981633974483

In this example, the variable angleInDegrees is set to 45. We then call the degreesToRadians function, passing in angleInDegrees as the argument. The function returns the corresponding angle in radians, which is then printed to the console.

Using a custom conversion function gives you more flexibility and control over the conversion process. You can easily modify the function to include additional logic or perform other calculations if needed.

By creating a custom conversion function, you can convert degrees to radians in JavaScript without relying on the built-in Math library. This can be particularly useful in certain scenarios where you have specific requirements or limitations.


Converting degrees to radians is important in trigonometric calculations because most mathematical functions in JavaScript, such as sine, cosine, and tangent, expect angles to be in radians. By converting degrees to radians, you ensure that your calculations are accurate and consistent.

In this article, we explored two methods for converting degrees to radians in JavaScript. The first method involved using the built-in Math library and its Math.radians() function. This function simplifies the conversion process and provides a quick solution for converting degrees to radians.

The second method showcased how to write a custom JavaScript function to convert degrees to radians. This method allows for more flexibility and customization, as you can define your own conversion logic based on your specific requirements.

By understanding the importance of converting degrees to radians and having knowledge of these two methods, you can confidently perform trigonometric calculations in JavaScript and ensure accurate results.