Excel ACOS Function

The Excel ACOS function returns arccosine (inverse cosine) of a number. It returns result expressed in radians.

The ACOS function is a built-in function in Excel that is categorized as a Math/Trig Function. It can be used as a worksheet function in Excel. As a worksheet function, the ACOS function can be used as part of a formula in a worksheet cell.

Syntax

ACOS(number)

Parameters

Return Value

Returns the arccosine of a value.

Notes

• To convert the result in degrees, multiply it by 180/PI() or use the DEGREES function.
• If the argument is outside of the range from -1 to 1, ACOS returns #NUM! error.
• If the argument is a non-numeric value, ACOS returns #VALUE! error.

Example: Using as Worksheet Function

The example below shows how to use the ACOS function as worksheet function.

Based on the Excel spreadsheet above, the output of the following worksheet formula will be:

=ACOS(B5)
Result: 3.141592654

=ACOS(B6)
Result: 2.094395102

=ACOS(B7)
Result: 1.875488981

=ACOS(B8)
Result: 1.570796327

=ACOS(B9)
Result: 1.266103673

=ACOS(B10)
Result: 1.047197551

=ACOS(B11)
Result: 0

Example: Convert Result to Degrees

To get the result from ACOS function in degrees, the result can be multiplied by 180/PI(). Alternatively, the angle can be converted into degrees by using DEGREES function. For example, to convert 2 radians into degrees, the following formula can be used:

=2 * 180/PI()
Result: 114.591559026165

=DEGREES(2)
Result: 114.591559026165

Example: PI() Function

A half-rotation (180°) in radians is equal to 3.142.. or 𝜋. A full-rotation (360°) in radians is equal to 6.283.. or 2𝜋. To get the value of 𝜋, Excel PI function can be used.

=PI()
Result: 3.14159265358979

=DEGREES(PI())
Result: 180