The Excel ATAN function returns the arctangent (inverse tangent) of a number — the angle whose tangent is that value. The result is in radians, from -π/2 to π/2.
Syntax
| Argument | Description | |
|---|---|---|
number | Required | The tangent value (any real number). ATAN returns the angle in radians, from -π/2 to π/2. |
How to use it
ATAN is the inverse of TAN: it converts a tangent value into the angle that produced it. Unlike ASIN and ACOS, ATAN accepts any real number — there is no domain limit:
The returned angle is always between -π/2 and π/2 (−90 to 90 degrees). Because ATAN only sees a single ratio, it cannot tell which quadrant the original point was in. When you have both an x and a y coordinate, use ATAN2 instead to get the full −180 to 180 range.
Slope to angle: a rise/run slope of 1 is a 45-degree incline — =DEGREES(ATAN(1)) confirms it. ATAN turns any slope into its angle of inclination.
Try it: interactive demo
Pick a ATAN example to see the formula and its result.
Practice workbook
Frequently asked questions
Why does ATAN(1) return 0.7854 rather than 45?
=DEGREES(ATAN(1)) to get 45.Does ATAN have a domain limit like ASIN?
When should I use ATAN2 instead of ATAN?
ATAN2 when you have separate x and y coordinates and need the angle in the correct quadrant (−180 to 180). ATAN only sees the ratio, so it cannot distinguish quadrants.What angle range does ATAN return?
-π/2 and π/2 radians (−90 to 90 degrees).Master functions like this in one day
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