`tan()` CSS function

The tan() CSS function is a trigonometric function that returns the tangent of a number, which is a value between −infinity and infinity. The function contains a single calculation that must resolve to either a <number> or an <angle> by interpreting the result of the argument as radians.

Syntax

css

/* Single <angle> values */
width: calc(100px * tan(45deg));
width: calc(100px * tan(0.125turn));
width: calc(100px * tan(0.785398163rad));

/* Single <number> values */
width: calc(100px * tan(0.5773502));
width: calc(100px * tan(1.732 - 1));

/* Other values */
width: calc(100px * tan(pi / 3));
width: calc(100px * tan(e));

Parameters

The tan(angle) function accepts only one value as its parameter.

angle: A calculation which resolves to a <number> or an <angle>. When specifying unitless numbers they are interpreted as a number of radians, representing an <angle>.

Return value

The tangent of an angle will always return a number between −∞ and +∞.

If angle is infinity, -infinity, or NaN, the result is NaN.
If angle is 0⁻, the result is 0⁻.
If angle is one of the asymptote values (such as 90deg, 270deg, etc.), the result is explicitly undefined. Authors must not rely on tan() returning any particular value for these inputs.

Formal syntax

<tan()> = 
  tan( <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

Drawing parallelograms

The tan() function can be used to draw a parallelogram with a given bounding box.

HTML

html

<div class="parallelogram"></div>

CSS

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

css

.parallelogram {
  --w: 400;
  --h: 200;
  --angle: 30deg;
  position: relative;
  width: calc(1px * var(--w));
  height: calc(1px * var(--h));
}
.parallelogram::before {
  content: "";
  position: absolute;
  width: calc(100% - 100% * var(--h) / var(--w) * tan(var(--angle)));
  height: 100%;
  transform-origin: 0 100%;
  transform: skewX(calc(0deg - var(--angle)));
  background-color: red;
}

Result

Specifications

CSS Values and Units Module Level 4

tan() CSS function