Learn How to Convert Angles From Degrees to Radians in Excel

What's trig got to do with it?

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Excel has a number of built-in trigonometric functions that make it easy to find the cosine, sine, and tangent of a right-angle triangle—a triangle containing an angle equal to 90 degrees. The only problem is that these functions require the angles are measured in radians rather than degrees, and while radians are a legitimate way of measuring angles based on the radius of a circle, they are not something most people work with on a regular basis.

To help the average spreadsheet user get around this problem, Excel has the RADIANS function, which makes it easy to convert degrees to radians.

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RADIANS Function Syntax and Arguments

Converting Angles from Degrees to Radians with Excel's RADIANS Function
Converting Angles from Degrees to Radians in Excel. © Ted French

A function's syntax refers to the layout of the function and includes the function's name, brackets, and arguments.

The syntax for the RADIANS function is:

= RADIANS ( Angle )

The Angle argument is the angle in degrees to be converted to radians. It can be entered as degrees or as a cell reference to the location of this data in a worksheet.

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Excel RADIANS Function Example

Refer to the image that accompanies this article as you follow along with this tutorial.

This example uses the RADIANS function to convert a 45-degree angle to radians. The information covers the steps used to enter the RADIANS function into cell B2 of the example worksheet.

Entering the RADIANS Function

Options for entering the function and its arguments include:

  • Typing the complete function: =RADIANS(A2) or =RADIANS(45) into cell B2
  • Selecting the function and its arguments using the RADIANS function dialog box

Although it is possible to enter the complete function manually, many people find it easier to use the dialog box, as it takes care of entering the function's syntax such as brackets and comma separators between arguments.

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Opening the Dialog Box

To enter the RADIANS function and arguments into cell B2 using the function's dialog box:

  1. Click on cell B2 in the worksheet. This is where the function will be located.
  2. Click on the Formulas tab of the ribbon menu.
  3. Choose Math & Trig from the ribbon to open the function drop-down list.
  4. Click on RADIANS in the list to bring up the function's dialog box.
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Entering the Function's Argument

 For some Excel functions, such as the RADIANS function, it is an easy matter to enter the actual data to be used for the argument directly into the dialog box.

However, it is usually best not to use actual data for a function's argument because doing so makes it harder to update the worksheet. This example enters the cell reference to the data as the function's argument.

  1. In the dialog box, click on the Angle line.
  2. Click on cell A2 in the worksheet to enter the cell reference as the function's argument.
  3. Click OK to complete the function and return to the worksheet. The answer 0.785398163, which is 45 degrees expressed in radians, appears in cell B2.

Click on cell B1 to see a complete function = RADIANS ( A2 ) appear in the formula bar above the worksheet.

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An Alternative

An alternative, as shown in row four of the example image, is to multiply the angle by the PI() function and then divide the result by 180 to get the angle in radians.

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Trigonometry and Excel

Trigonometry focuses on the relationships between the sides and the angles of a triangle, and while many of us do not need to use it on a daily basis, trigonometry has applications in a number of fields including astronomy, physics, engineering, and surveying.

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Historical Note

Apparently, Excel's trig functions use radians rather than degrees because when the program was first created, the trig functions were designed to be compatible with the trig functions in the spreadsheet program Lotus 1-2-3, which also used radians and which dominated the PC spreadsheet software market at the time.