Excel ACOS Function

The ACOS function returns the inverse cosine of a value. Input to the arc-cosine function must be between -1 and 1, inclusive. Geometrically, given the ratio of a triangle's adjacent side over its hypotenuse, the function returns the angle of the triangle. For example, given a ratio of 0.5 the function returns the angle of 1.047 radians.

=ACOS(0.5) // Returns 1.047 radians

Convert Result to Degrees

To convert the result from radians to degrees, multiply the result by 180/PI() or use the DEGREES function. For example, the convert the result of ACOS(0.5) to degrees, you can use either formula below:

=ACOS(0.5)*180/PI() // Returns 60 degrees
=DEGREES(ACOS(0.5)) // Returns 60 degrees

Explanation

The graph of ACOS visualizes the output of the function in the range from -1 to 1. ACOS is the inverse of the COS function. However, because COS is a periodic function, the output of ACOS is limited to the range from 0 to π.

Graph courtesy of wumbo.net.