Sass math.asin()

Definition and Usage

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

Syntax

@use "sass:math";

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

math.asin(0.5);  // 30deg
math.asin(1);    // 90deg
math.asin(0);    // 0deg
math.asin(-0.5); // -30deg
math.asin(-1);   // -90deg
math.asin(2);    // NaN angle (out of range)

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

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

Domain and Range

Keep the sine domain in mind before calling asin:

Related Functions

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

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.asin(0.5); // 30deg

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

.basic {
  --half: 30deg;
}

@use "sass:math";

.range {
  --one: #{math.asin(1)};
  --zero: #{math.asin(0)};
  --neg-half: #{math.asin(-0.5)};
  --neg: #{math.asin(-1)};
}

.range {
  --one: 90deg;
  --zero: 0deg;
  --neg-half: -30deg;
  --neg: -90deg;
}

@use "sass:math";

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

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

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

@use "sass:math";

.roundtrip {
  --back-num: #{math.sin(math.asin(0.5))};
  --back-ang: #{math.asin(math.sin(30deg))};
  --acos: #{math.acos(0.5)};
}

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

@use "sass:math";

$sin: 0.5;

.angle {
  --deg: #{math.asin($sin)};
  transform: rotate(math.asin($sin));
}

.angle {
  --deg: 30deg;
  transform: rotate(30deg);
}

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 (-90deg…90deg)
4. Clamp noisy inputs before asin
5. Use math.sin for the forward transform