`acos()` CSS function

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

/* 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> | '/' <number> ]*

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

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

Examples

Rotate elements

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

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;
}

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));
}

Result

Specifications

Browser compatibility

See also

• sin()
• cos()
• tan()
• asin()
• atan()
• atan2()