acos()

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 <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 <number> between -1 and 1.

Return value

The inverse cosine of an number will always return an <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

<acos()> =
acos( <calc-sum> )

<calc-sum> =
<calc-product> [ [ '+' | '-' ] <calc-product> ]*

<calc-product> =
<calc-value> [ [ '*' | '/' ] <calc-value> ]*

<calc-value> =
<number> |
<dimension> |
<percentage> |
<calc-constant> |
( <calc-sum> )

<calc-constant> =
e |
pi |
infinity |
-infinity |
NaN

Examples

Rotate elements

The acos() 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;
}
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));
}

Specifications

Specification
CSS Values and Units Module Level 4
# trig-funcs

Browser compatibility

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