Math.atan()

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

The Math.atan() static method returns the inverse tangent (in radians) of a number, that is

\mathtt{\operatorname{Math.atan}(x)} = \arctan(x) = \text{the unique } y \in \left[-\frac{\pi}{2}, \frac{\pi}{2}\right] \text{ such that } \tan(y) = x

Try it

// Calculates angle of a right-angle triangle in radians
function calcAngle(opposite, adjacent) {
  return Math.atan(opposite / adjacent);
}

console.log(calcAngle(8, 10));
// Expected output: 0.6747409422235527

console.log(calcAngle(5, 3));
// Expected output: 1.0303768265243125

Syntax

Math.atan(x)

Parameters

x: A number.

Return value

The inverse tangent (angle in radians between $-\frac{\pi}{2}$ and $\frac{\pi}{2}$ , inclusive) of x. If x is Infinity, it returns $\frac{\pi}{2}$ . If x is -Infinity, it returns $-\frac{\pi}{2}$ .

Description

Because atan() is a static method of Math, you always use it as Math.atan(), rather than as a method of a Math object you created (Math is not a constructor).

Examples

Using Math.atan()

Math.atan(-Infinity); // -1.5707963267948966 (-π/2)
Math.atan(-0); // -0
Math.atan(0); // 0
Math.atan(1); // 0.7853981633974483  (π/4)
Math.atan(Infinity); // 1.5707963267948966  (π/2)

// The angle that the line (0,0) -- (x,y) forms with the x-axis in a Cartesian coordinate system
const theta = (x, y) => Math.atan(y / x);

Note that you may want to avoid the theta function and use Math.atan2() instead, which has a wider range (between -π and π) and avoids outputting NaN for cases such as when x is 0.

Specifications

Specification
ECMAScript® 2026 Language Specification # sec-math.atan

Browser compatibility

	Desktop					Mobile						Server
	Chrome	Edge	Firefox	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet	WebView Android	Deno	Node.js
`atan`	1	12	1	3	1	18	4	10.1	1	1.0	4.4	1.0	0.10.0