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ATAN Function

Excel 2007+

Summary

The ATAN function in Excel calculates the arctangent (inverse tangent) of a specified number, returning the angle in radians whose tangent equals that number. This trigonometric function is essential for mathematical computations, geometric calculations, and engineering applications requiring angle determination from tangent values.

Syntax

ATAN(number)

Parameters

Parameter	Type	Required	Description
number	`Number`	Yes	The tangent value representing the ratio of opposite over adjacent sides in a right triangle

Using the ATAN Function

ATAN is commonly used in trigonometry, physics, and engineering to find angles when the tangent ratio is known. It serves as a core building block for more complex calculations involving coordinate geometry, vectors, and waveform analysis. Results are in radians, making it compatible with other Excel trig functions.

Common ATAN Examples

Basic Arctangent Calculation

=ATAN(1)

Returns the arctangent of 1 (π/4 radians, approximately 0.7854) which represents a 45-degree angle.

Convert to Degrees Using PI

=ATAN(1)*180/PI()

Converts arctangent of 1 from radians to degrees, yielding exactly 45°.

Convert Using DEGREES Function

=DEGREES(ATAN(1))

Uses Excel's DEGREES function for clean radian-to-degree conversion, result is 45.

Frequently Asked Questions

ATAN returns angles in radians from -π/2 (-1.5708) to π/2 (1.5708).

Multiply by 180/PI() or wrap with DEGREES(ATAN(number)).

Yes, negative inputs return negative angles in the proper quadrant.

Common Errors and Solutions

#VALUE!

Cause: Non-numeric input provided

Solution: Ensure the number argument contains a valid numeric value

#NUM!

Cause: Input outside acceptable range (rare for ATAN)

Solution: ATAN accepts all real numbers; check for other formula errors

Notes

Output is always in radians, never degrees
Given tan(θ) = number, ATAN returns θ
Perfect for right-triangle opposite/adjacent calculations
Use ATAN2 for precise quadrant determination with x,y coordinates

Compatibility

Available in: Excel 2007, Excel 2010, Excel 2013, Excel 2016, Excel 2019, Excel 2021, Microsoft 365

Not available in:

Content last reviewed: December 9, 2025
Update frequency: As needed
Excel versions tested: Excel 2007+