Math.acos()
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.
TheMath.acos() static method returns the inverse cosine (in radians) of a number. That is,
Try it
// Calculates angle of a right-angle triangle in radiansfunction calcAngle(adjacent, hypotenuse) { return Math.acos(adjacent / hypotenuse);}console.log(calcAngle(8, 10));// Expected output: 0.6435011087932843console.log(calcAngle(5, 3));// Expected output: NaNSyntax
js
Math.acos(x)Parameters
xA number between -1 and 1, inclusive, representing the angle's cosine value.
Return value
The inverse cosine (angle in radians between 0 and π, inclusive) ofx. Ifx is less than -1 or greater than 1, returnsNaN.
Description
Becauseacos() is a static method ofMath, you always use it asMath.acos(), rather than as a method of aMath object you created (Math is not a constructor).
Examples
Using Math.acos()
js
Math.acos(-2); // NaNMath.acos(-1); // 3.141592653589793 (π)Math.acos(0); // 1.5707963267948966 (π/2)Math.acos(0.5); // 1.0471975511965979 (π/3)Math.acos(1); // 0Math.acos(2); // NaNSpecifications
| Specification |
|---|
| ECMAScript® 2026 Language Specification # sec-math.acos |