Atan2 function

This article describes the formula syntax and usage of the ATAN2 function in Microsoft Excel.

Description

Returns the arctangent, or inverse tangent, of the specified x- and y-coordinates. The arctangent is the angle from the x-axis to a line containing the origin (0, 0) and a point with coordinates (x_num, y_num). The angle is given in radians between -pi and pi, excluding -pi.

Syntax

ATAN2(x_num, y_num)

The ATAN2 function syntax has the following arguments:

• X_num    Required. The x-coordinate of the point.

• Y_num    Required. The y-coordinate of the point.

Remarks

• A positive result represents a counterclockwise angle from the x-axis; a negative result represents a clockwise angle.

• ATAN2(a,b) equals ATAN(b/a), except that a can equal 0 in ATAN2.

• If both x_num and y_num are 0, ATAN2 returns the #DIV/0! error value.

• To express the arctangent in degrees, multiply the result by 180/PI( ) or use the DEGREES function.

Example

Copy the example data in the following table, and paste it in cell A1 of a new Excel worksheet. For formulas to show results, select them, press F2, and then press Enter. If you need to, you can adjust the column widths to see all the data.

Formula	Description	Result
=ATAN2(1, 1)	Arctangent of the point 1,1 in radians, pi/4	0.785398163
=ATAN2(-1, -1)	Arctangent of the point -1,-1 in radians, -3*pi/4	-2.35619449
=ATAN2(-1, -1)*180/PI()	Arctangent of the point 1,1 in degrees	-135
=DEGREES(ATAN2(-1, -1))	Arctangent of the point 1,1 in degrees	-135