`atan()` CSS function

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

undefined

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));
}

Result

Specifications

CSS Values and Units Module Level 4

atan() CSS function