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 and , inclusive) of x. If x is Infinity, it returns . If x is -Infinity, it returns .

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® 2027 Language Specification # sec-math.atan

Browser compatibility

Help improve MDN

Yes No

Learn how to contribute

This page was last modified on Dec 29, 2025 by MDN contributors.