`atan()` 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 atan() CSS function is a trigonometric function that returns the inverse tangent of a number between -∞ and +∞. The function contains a single calculation that returns an <angle> between -90deg and 90deg.

Syntax

css

/* Single <number> values */
transform: rotate(atan(1));
transform: rotate(atan(4 * 50));

/* Other values */
transform: rotate(atan(pi / 2));
transform: rotate(atan(e * 3));

Parameters

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

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

Return value

The inverse tangent of a number will always return an <angle> between -90deg and 90deg.

If number is 0⁻, the result is 0⁻.
If number is +∞ the result is 90deg.
If number is -∞ the result is -90deg.

That is:

atan(-infinity) representing -90deg.
atan(-1) representing -45deg
atan(0) representing 0deg
atan(1) representing 45deg
atan(infinity) representing 90deg.

Formal syntax

<atan()> = 
  atan( <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 atan() 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(atan(-99999));
}
div.box-2 {
  transform: rotate(atan(-1));
}
div.box-3 {
  transform: rotate(atan(0));
}
div.box-4 {
  transform: rotate(atan(1));
}
div.box-5 {
  transform: rotate(atan(99999));
}