## Excel ACOS Function

The ACOS function calculates the arccosine (inverse cosine) of a number, and returns an angle, in radians, in the range from 0 (zero) to π (pi). =ACOS(number)

#### Arguments

• number (required): The value for which you want to calculate the arccosine. Note: The number must be between -1 and 1.

#### Return Value

The ACOS function returns a numeric value.

#### Function Notes

• The result is an angle expressed in radians. To convert the angle from radians to degrees, use the DEGREES function, or multiply the result by 180/PI().
• ACOS returns the #NUM! error if number < -1 or number > 1.
• ACOS returns the #VALUE! error if number is not numeric.

#### Example

To calculate the arccosine (inverse cosine) of the numbers listed in the table as shown below, please copy or enter the below formula in the top cell (D6) of the result list, and press Enter to get the result. Then select the result cell, and drag the fill handle (the small square in the lower-right corner of the selected cell) down to apply the formula to the below cells.

=ACOS(B6) Instead of a cell reference, you can type the actual number value in the formula as shown below.

=ACOS(-1)

Note that the results are angles expressed in radians. You can nest the ACOS function into a DEGREES function to convert the angles from radians to degrees as shown below.

=DEGREES(ACOS(-1))

Alternatively, you can multiply ACOS by 180/PI().

=ACOS(-1)*180/PI()

#### Related functions

Excel ACOSH Function

The ACOSH function returns the inverse hyperbolic cosine of a number.

Excel DEGREES Function

The DEGREES function converts an angle in radians to an angle in degrees.

Excel PI Function

The PI function returns the number 3.14159265358979 of the mathematical constant called pi.

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