Sass math.log()

Definition and Usage

math.log($number, $base: null) returns the logarithm of $number with respect to $base. If $base is null (the default), Sass calculates the natural log (base e). Both $number and $base must be unitless. Load it with @use "sass:math" on Dart Sass 1.25+.

Syntax

@use "sass:math";

math.log($number, $base: null); //=> unitless number

math.log(10);     // 2.302585093  (natural log)
math.log(10, 10); // 1
math.log(8, 2);   // 3

math.log(math.$e); // 1  (ln(e))

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

Pattern: ensure unitless input → choose natural log or a base → use the result as a scale exponent or step count. Related: math.pow, math.sqrt, math.div.

Bases and Inputs

How the second argument changes the result:

Related Functions

Load with @use "sass:math". Previous: math.is-unitless(). Next: math.max(). Also: math.pow(), math.sqrt(), math.div(), math.percentage().

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.log(10); // 2.302585093

.basic {
  --ln: #{math.log(10)};
}

.basic {
  --ln: 2.302585093;
}

@use "sass:math";

@debug math.log(10, 10); // 1

.base {
  --log10: #{math.log(10, 10)};
}

.base {
  --log10: 1;
}

@use "sass:math";

.binary {
  --two: #{math.log(8, 2)};
  --e: #{math.log(math.$e)};
}

.binary {
  --two: 3;
  --e: 1;
}

@use "sass:math";

.roundtrip {
  --pow: #{math.pow(10, math.log(10, 10))};
}

.roundtrip {
  --pow: 10;
}

@use "sass:math";

$ratio: 100;

.scale {
  --steps: #{math.log($ratio, 10)};
  opacity: math.div(math.log(8, 2), 10);
}

.scale {
  --steps: 2;
  opacity: 0.3;
}

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. Ensure $number (and $base) are unitless
3. Omit $base for natural log; pass a base for log_b
4. Pair with math.pow for round-trips
5. Use math.is-unitless before logging unknown tokens