The atan2() CSS function is a trigonometric function that returns the inverse tangent of two values between -infinity and infinity. The function accepts two arguments and returns the number of radians representing an <angle> between -180deg and 180deg.

Syntax

/* Two <number> values */
transform: rotate(atan2(3, 2));

/* Two <dimension> values */
transform: rotate(atan2(1rem, -0.5rem));

/* Two <percentage> values */
transform: rotate(atan2(20%, -30%));

/* Other values */
transform: rotate(atan2(pi, 45));
transform: rotate(atan2(e, 30));

Parameters

The atan2(y, x) function accepts two comma-separated values as its parameters. Each value can be a <number>, a <dimension>, or a <percentage>. Both values must be of the same type, although if they are <dimension> they can be of different units (example: atan2(100px, 5vw) is valid).

y

The y-coordinate of the point. A calculation which resolves to a <number>, a <dimension>, or a <percentage>.

x

The x-coordinate of the point. A calculation which resolves to a <number>, a <dimension>, or a <percentage>.

Return value

Given two values x and y, the function atan2(y, x) calculates and returns the <angle> between the positive x-axis and the ray from the origin to the point (x, y).

Formal syntax

<atan2()> = 
  atan2( <calc-sum> , <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 atan2() function can be used to rotate elements as it return 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

div.box {
  width: 100px;
  height: 100px;
  background: linear-gradient(orange, red);
}
div.box-1 {
  transform: rotate(atan2(3, 2));
}
div.box-2 {
  transform: rotate(atan2(3%, -2%));
}
div.box-3 {
  transform: rotate(atan2(-1, 0.5));
}
div.box-4 {
  transform: rotate(atan2(1, 0.5));
}
div.box-5 {
  transform: rotate(atan2(1rem, -0.5rem));
}

Result

Specifications

Browser compatibility

See also

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