index.md

title	slug	page-type	browser-compat
acos()	Web/CSS/acos	css-function	css.types.acos

{{CSSRef}}

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 the number of radians representing an {{cssxref("<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));

Parameter

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

• number
  • : A calculation which resolves to a {{cssxref("<number>")}} between -1 and 1.

Return value

The inverse cosine of an number will always return an {{cssxref("<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

{{CSSSyntax}}

Examples

Rotate elements

The acos() function can be used to {{cssxref("transform-function/rotate", "rotate")}} elements as it return an {{cssxref("<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

{{EmbedLiveSample('Rotate elements', '100%', '200px')}}

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also

• {{CSSxRef("sin")}}
• {{CSSxRef("cos")}}
• {{CSSxRef("tan")}}
• {{CSSxRef("asin")}}
• {{CSSxRef("atan")}}
• {{CSSxRef("atan2")}}