ACOS Function

Originally published at: ACOS Function in Excel -

The ACOS Function returns the inverse cosine of a number in radians. The number must be between -1 and 1.

If the number is outside -1 to 1, Excel will return a #NUM error.




  • number – Number between -1 and 1.

PV Function Usage Example:

Below is an example of how to use the ACOS Function. In the below example, we are looking for the inverse cosine of .85 and -.65. The result in radians in shown below.

A Radian is a unit of angle, equal to an angle at the center of a circle whose arc is equal in length to the radius. Please see the slide below.



Result: 0.554811033 Radians

=ACOS (-.65)

Result: 2.278380764 Radian

Radian to Degrees




You can easily convert the returned Radian from the ACOS function to degrees by using the DEGREES function and PI function as shown below.