Sass math.acos()

Definition and Usage

math.acos($number) returns the arccosine of $number in deg. $number must be unitless. Load it with @use "sass:math" on Dart Sass 1.25+.

Syntax

@use "sass:math";

math.acos($number); //=> angle in deg

math.acos(0.5); // 60deg
math.acos(1);   // 0deg
math.acos(0);   // 90deg
math.acos(-1);  // 180deg
math.acos(2);   // NaN angle (out of range)

// Module API — prefer math.acos after @use "sass:math"

Pattern: compute a cosine ratio → math.acos for a CSS angle → compare with math.asin / math.atan when the geometry differs.

Domain and Range

Keep the cosine domain in mind before calling acos:

Related Functions

Load with @use "sass:math". Previous: math.abs(). Next: math.asin(). Also: math.cos(), math.atan(), math.atan2(), math.sin().

SCSS Examples

Examples target Dart Sass 1.25+ with @use "sass:math". Open View Compiled CSS for verified output (matches official Sass docs samples).

@use "sass:math";

@debug math.acos(0.5); // 60deg

.basic {
  --half: #{math.acos(0.5)};
}

.basic {
  --half: 60deg;
}

@use "sass:math";

.range {
  --one: #{math.acos(1)};
  --zero: #{math.acos(0)};
  --neg: #{math.acos(-1)};
}

.range {
  --one: 0deg;
  --zero: 90deg;
  --neg: 180deg;
}

@use "sass:math";

@debug math.acos(2); // NaN angle (docs: NaNdeg)

.nan {
  --bad: #{math.acos(2)};
}

.nan {
  --bad: calc(NaN * 1deg);
}

@use "sass:math";

.roundtrip {
  --back-num: #{math.cos(math.acos(0.5))};
  --back-ang: #{math.acos(math.cos(60deg))};
  --asin: #{math.asin(0.5)};
}

.roundtrip {
  --back-num: 0.5;
  --back-ang: 60deg;
  --asin: 30deg;
}

@use "sass:math";

$cos: 0.5;

.angle {
  --deg: #{math.acos($cos)};
  transform: rotate(math.acos($cos));
}

.angle {
  --deg: 60deg;
  transform: rotate(60deg);
}

Sass Support

Prefer the module form with Dart Sass 1.25+.

Compile with the Dart Sass CLI.

Key Takeaways

Compile Notes

Practical checklist:

1. @use "sass:math"
2. Pass a unitless ratio in -1…1
3. Expect a deg angle (0deg…180deg)
4. Clamp noisy inputs before acos
5. Use math.cos for the forward transform