`acos()` CSS function

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since March 2023.

The acos() CSS function is a trigonometric function that returns the inverse cosine of a number between -1 and 1. The function contains a single calculation that returns an <angle> between 0deg and 180deg.

Syntax

css

/* Single <number> values */
transform: rotate(acos(-0.2));
transform: rotate(acos(2 * 0.125));

/* Other values */
transform: rotate(acos(pi / 5));
transform: rotate(acos(e / 3));

Parameters

The acos(number) function accepts only one value as its parameter.

number: A calculation which resolves to a <number> between -1 and 1.

Return value

The inverse cosine of a number will always return an <angle> between 0deg and 180deg.

If number is less than -1 or greater than 1, the result is NaN.
If number is exactly 1, the result is 0.

Formal syntax

<acos()> = 
  acos( <calc-sum> )  

<calc-sum> = 
  <calc-product> [ [ '+' | '-' ] <calc-product> ]*  

<calc-product> = 
  <calc-value> [ [ '*' | / ] <calc-value> ]*  

<calc-value> = 
  <number>        |
  <dimension>     |
  <percentage>    |
  <calc-keyword>  |
  ( <calc-sum> )  

<calc-keyword> = 
  e          |
  pi         |
  infinity   |
  -infinity  |
  NaN

Examples

Rotate elements

The acos() function can be used to rotate elements as it return an <angle>.

HTML

html

<div class="box box-1"></div>
<div class="box box-2"></div>
<div class="box box-3"></div>
<div class="box box-4"></div>
<div class="box box-5"></div>

CSS

body {
  height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 50px;
}

css

div.box {
  width: 100px;
  height: 100px;
  background: linear-gradient(orange, red);
}
div.box-1 {
  transform: rotate(acos(1));
}
div.box-2 {
  transform: rotate(acos(0.5));
}
div.box-3 {
  transform: rotate(acos(0));
}
div.box-4 {
  transform: rotate(acos(-0.5));
}
div.box-5 {
  transform: rotate(acos(-1));
}