The Excel ATAN Function


The Arctangent is the inverse of the tangent.

Therefore, for the simple right-angled triangle below, the arctangent of the opposite side, o, divided by the adjacent side, a, is equal to the angle θ.

Right-Angled Triangle

I.e. for the triangle above,

Arctangent Equation
The Inverse trig. functions are discussed further on the Wikipedia Inverse Trigonometric Functions Page

Basic Description

The Excel ATAN function calculates the arctangent (i.e. the inverse tangent) of a given number, and returns an angle, in radians, between -π/2 and +π/2.

The syntax of the function is:

ATAN( number )

Where the number argument is the value, for which you want to calculate the arctangent.

Converting from Radians to Degrees

If you want the angle returned by the Atan function to be expressed in degrees, you can convert it, using the Excel Degrees function:

=DEGREES( radians )
An example of this is provided below.

Excel Atanh Function Examples

The following spreadsheet shows the Excel Atan Function, used to calculate the arctangent of four different values.

1=ATAN( -1 )
2=ATAN( 0 )
3=ATAN( 1 )
4=DEGREES( ATAN( 1 ) )
1-0.785398163 - Result is -π/4 radians
20 - Result is 0 radians
30.785398163 - Result is π/4 radians
445 - Result is 45 degrees

Note that in cell A4, the Excel Degrees function is used to convert the calculated angle from radians to degrees.

For further information and examples of the Excel Atan function, see the Microsoft Office website.

Atan Function Error

If you get an error from the Excel Atan Function, this is likely to be the #VALUE! error:

Common Error
#VALUE!-Occurs if the supplied number argument is non-numeric.