Excel COS Function

The COS function returns the cosine of an angle provided in radians. In geometric terms, the cosine of an angle returns the ratio of a right triangle's adjacent side over its hypotenuse. For example, the cosine of PI()/6 radians (30°) returns the ratio 0.866.

=COS(PI()/6) // Returns 0.886

Using Degrees

To supply an angle to COS in degrees, multiply the angle by PI()/180 or use the RADIANS function to convert to radians. For example, to get the COS of 60 degrees, you can use either formula below:

=COS(60*PI()/180)
=COS(RADIANS(60))

Explanation

The graph of cosine above visualizes the output of the function for all angles from 0 to a full rotation. Geometrically, the function returns the x-component of the point corresponding to an angle on the unit circle. Since the cosine of an angle returns a ratio, the output of the function will always be in the range [-1, 1].

Graph courtesy of wumbo.net