The Excel TAN function returns the tangent of angle given in radians. To supply an angle to TAN in degrees, multiply the angle by PI()/180 or use the RADIANS function to convert to radians.
Get the tangent of an angle
The tangent value.
number - The angle in radians for which you want the tangent.
The TAN function returns the tangent of an angle provided in radians. In geometric terms, the tangent of an angle returns the ratio of a right-triangle's opposite side over its adjacent side. For example, the the tangent of PI()/4 (45°) returns the ratio of 1.0.
The graph of the tangent function, shown above, visualizes the output of the function for angles from 0 to a full rotation corresponding to the range [0, 2π]. The function has two vertical asymptotes within the range [0, 2π] where the output diverges to infinity. The tangent function can be equivalently defined in terms of SIN and COS: