Calculations

Calculations are how Sass represents the calc() function, as well as similar functions like clamp(), min(), and max(). Sass will simplify these as much as possible, even if they’re combined with one another.

Dart Sass: since 1.40.0
LibSass: ✗
Ruby Sass: ✗

LibSass, Ruby Sass, and versions of Dart Sass prior to 1.40.0 parse calc() as a special function like element().

LibSass, Ruby Sass, and versions of Dart Sass prior to 1.31.0 parse clamp() as a plain CSS function rather than supporting special syntax within it. Versions of Dart Sass between 1.31.0 and 1.40.0 parse clamp() as a special function like element().

Dart Sass: since 1.67.0
LibSass: ✗
Ruby Sass: ✗

Versions of Dart Sass between 1.40.0 and 1.67.0 don’t allow multiple values in calculations that aren’t separated by an operator, even in cases like calc(1 var(--plus-two)) which is valid CSS (since --plus-two can be defined to be + 2).

As of Dart Sass 1.67.0, multiple values in a calculation can be separated by spaces as long as every other value evaluates to an unquoted string (such as a var() expression or the unquoted string "+ 2").

  SCSS

  Sass

  SCSS Syntax@debug calc(400px + 10%); // calc(400px + 10%)
@debug calc(400px / 2); // 200px
@debug min(100px, calc(1rem + 10%)); // min(100px, 1rem + 10%)

  Sass Syntax@debug calc(400px + 10%)  // calc(400px + 10%)
@debug calc(400px / 2)  // 200px
@debug min(100px, calc(1rem + 10%)) ; // min(100px, 1rem + 10%)

Calculations use a special syntax that’s different from normal SassScript. It’s the same syntax as the CSS calc(), but with the additional ability to use Sass variables and call Sass functions. This means that / is always a division operator within a calculation!

💡 Fun fact:

The arguments to a Sass function call use the normal Sass syntax, rather than the special calculation syntax!

You can also use interpolation in a calculation. However, if you do, no operations that involve that interpolation will be simplified or type-checked, so it’s easy to end up with extra verbose or even invalid CSS. Rather than writing calc(10px + #{$var}), just write calc(10px + $var)!

SimplificationSimplification permalink

Sass will simplify adjacent operations in calculations if they use units that can be combined at compile-time, such as 1in + 10px or 5s * 2. If possible, it’ll even simplify the whole calculation to a single number—for example, clamp(0px, 30px, 20px) will return 20px.

⚠️ Heads up!

This means that a calculation expression won’t necessarily always return a calculation! If you’re writing a Sass library, you can always use the meta.type-of() function to determine what type you’re dealing with.

Calculations will also be simplified within other calculations. In particular, if a calc() end up inside any other calculation, the function call will be removed and it’ll be replaced by a plain old operation.

  SCSS

  Sass

  CSS

  SCSS Syntax$width: calc(400px + 10%);

.sidebar {
  width: $width;
  padding-left: calc($width / 4);
}

  Sass Syntax$width: calc(400px + 10%)

.sidebar
  width: $width
  padding-left: calc($width / 4)


  CSS Output.sidebar {
  width: calc(400px + 10%);
  padding-left: calc((400px + 10%) / 4);
}

OperationsOperations permalink

You can’t use calculations with normal SassScript operations like + and *. If you want to write some math functions that allow calculations just write them within their own calc() expressions—if they’re passed a bunch of numbers with compatible units, they’ll return plain numbers as well, and if they’re passed calculations they’ll return calculations.

This restriction is in place to make sure that if calculations aren’t wanted, they throw an error as soon as possible. Calculations can’t be used everywhere plain numbers can: they can’t be injected into CSS identifiers (such as .item-#{$n}), for example, and they can’t be passed to Sass’s built-in math functions. Reserving SassScript operations for plain numbers makes it clear exactly where calculations are allowed and where they aren’t.

  SCSS

  Sass

  SCSS Syntax$width: calc(100% + 10px);
@debug $width * 2; // Error!
@debug calc($width * 2); // calc((100% + 10px) * 2);

  Sass Syntax$width: calc(100% + 10px);
@debug $width * 2; // Error!
@debug calc($width * 2); // calc((100% + 10px) * 2);

ConstantsConstants permalink

Dart Sass: since 1.60.0
LibSass: ✗
Ruby Sass: ✗

Calculations can also contain constants, which are written as CSS identifiers. For forwards-compatibility with future CSS specs, all identifiers are allowed, and by default they’re just treated as unquoted strings that are passed-through as-is.

  SCSS

  Sass

  SCSS Syntax@debug calc(h + 30deg); // calc(h + 30deg);

  Sass Syntax@debug calc(h + 30deg)  // calc(h + 30deg);

Sass automatically resolves a few special constant names that are specified in CSS to unitless numbers:

pi is a shorthand for the mathematical constant π.
e is a shorthand for the mathematical constant e.
infinity, -infinity, and NaN represent the corresponding floating-point values.

  SCSS

  Sass

  SCSS Syntax@use 'sass:math';

@debug calc(pi); // 3.1415926536
@debug calc(e);  // 2.7182818285
@debug calc(infinity) > math.$max-number;  // true
@debug calc(-infinity) < math.$min-number; // true

  Sass Syntax@use 'sass:math'

@debug calc(pi)  // 3.1415926536
@debug calc(e)   // 2.7182818285
@debug calc(infinity) > math.$max-number   // true
@debug calc(-infinity) < math.$min-number  // true

Calculation FunctionsCalculation Functions permalink

Dart Sass: since 1.65.0
LibSass: ✗
Ruby Sass: ✗

Versions of Dart Sass 1.65.0 and later except 1.66.x handle the execution of these calculation functions: round(), mod(), rem(), sin(), cos(), tan(), asin(), acos(), atan(), atan2(), pow(), sqrt(), hypot(), log(), exp(), abs(), and sign().

In Dart Sass 1.65.x, any function call whose name matched a calculation function was always parsed as a calculation function. This broke some existing user-defined functions, so support for the new calculation functions was removed in 1.66.0 until it could be added back without breaking existing behavior in 1.67.0.

Sass parses the following functions as calculations:

Comparison Functions: min(), max(), and clamp()
Stepped Value Functions: round(), mod(), and rem().
Trigonometric Functions: sin(), cos(), tan(), asin(), acos(), atan(), and atan2().
Exponential Functions: pow(), sqrt(), hypot(), log(), and exp().
Sign-Related Functions: abs() and sign().

💡 Fun fact:

If you’ve defined a Sass function with the same name as a calculation function, Sass will always call your function instead of creating a calculation value.

Legacy Global FunctionsLegacy Global Functions permalink

CSS added support for mathematical expressions in Values and Units Level 4. However, Sass supported its own round(), abs(), min() and max() long before this, and it needed to be backwards-compatible with all those existing stylesheets. This led to the need for extra-special syntactic cleverness.

If a call to round(), abs(), min(), or max() is a valid calculation expression, it will be parsed as a calculation. But as soon as any part of the call contains a SassScript feature that isn’t supported in a calculation, like the modulo operator, it’s parsed as a call to the appropriate Sass math function instead.

Since calculations are simplified to numbers when possible anyway, the only substantive difference is that the Sass functions only support units that can be combined at build time, so min(12px % 10, 10%) will throw an error.

⚠️ Heads up!

Other calculations don’t allow unitless numbers to be added to, subtracted from, or compared to numbers with units. min(), max(), abs() and single-argument round() are different, though: for backwards-compatibility with the global Sass legacy functions which allow unit/unitless mixing for historical reasons, these units can be mixed as long as they’re contained directly within a min(), max(), abs(), or single-argument round() calculation.

For instance, min(5 + 10px, 20px) will result in 15px. However sqrt(5 + 10px) will throw an error, as sqrt(5 + 10px) was never a global Sass function, and these are incompatible units.

`min()` and `max()`min() and max() permalink

Dart Sass: since >=1.11.0 <1.42.0
LibSass: ✗
Ruby Sass: ✗

LibSass, Ruby Sass, and versions of Dart Sass prior to 1.11.0 always parse min() and max() as Sass functions. To create a plain CSS min() or max() call for those implementations, you can write something like unquote("min(#{$padding}, env(safe-area-inset-left))") instead.

CSS added support for min() and max() functions in Values and Units Level 4, from where they were quickly adopted by Safari to support the iPhoneX. Since we already supported min() and max() as legacy Sass functions, we had to implement logic for backwards-compatibility and for support as CSS functions.

Versions of Dart Sass between 1.11.0 and 1.40.0, and between 1.40.1 and 1.42.0 parse min() and max() functions as special functions if they’re valid plain CSS, but parse them as Sass functions if they contain Sass features other than interpolation, like variables or function calls.

Dart Sass 1.41.0 parses min() and max() functions as calculations, but doesn’t allow unitless numbers to be combined with numbers with units. This was backwards-incompatible with the global min() and max() functions, so that behavior was reverted.

  SCSS

  Sass

  CSS

  SCSS Syntax$padding: 12px;

.post {
  // Since these max() calls are valid calculation expressions, they're
  // parsed as calculations.
  padding-left: max($padding, env(safe-area-inset-left));
  padding-right: max($padding, env(safe-area-inset-right));
}

.sidebar {
  // Since these use the SassScript-only modulo operator, they're parsed as
  // SassScript function calls.
  padding-left: max($padding % 10, 20px);
  padding-right: max($padding % 10, 20px);
}

  Sass Syntax$padding: 12px

.post
  // Since these max() calls are valid calculation expressions, they're
  // parsed as calculations.
  padding-left: max($padding, env(safe-area-inset-left))
  padding-right: max($padding, env(safe-area-inset-right))


.sidebar
  // Since these use the SassScript-only modulo operator, they're parsed as
  // SassScript function calls.
  padding-left: max($padding % 10, 20px)
  padding-right: max($padding % 10, 20px)


  CSS Output.post {
  padding-left: max(12px, env(safe-area-inset-left));
  padding-right: max(12px, env(safe-area-inset-right));
}

.sidebar {
  padding-left: 20px;
  padding-right: 20px;
}

`round()`round() permalink

Dart Sass: since 1.65.0
LibSass: ✗
Ruby Sass: ✗

LibSass, Ruby Sass, and versions of Dart Sass prior to 1.65.0, as well as Dart Sass 1.66.x, always parse round() as a Sass function. To use a plain CSS function for those implementations, you can write something like round(#{$strategy, $number, $step}) instead.

The round(<strategy>, number, step) function accepts an optional rounding strategy, a value to be rounded and a rounding interval step. strategy should be nearest, up, down, or to-zero.

  SCSS

  Sass

  CSS

  SCSS Syntax$number: 12.5px;
$step: 15px;

.post-image {
  // Since these round() calls are valid calculation expressions, they're
  // parsed as calculations.
  padding-left: round(nearest, $number, $step);
  padding-right: round($number + 10px);
  padding-bottom: round($number + 10px, $step + 10%);
}

  Sass Syntax$number: 12.5px
$step: 15px

.post-image
  // Since these round() calls are valid calculation expressions, they're
  // parsed as calculations.
  padding-left: round(nearest, $number, $step)
  padding-right: round($number + 10px)
  padding-bottom: round($number + 10px, $step + 10%)


  CSS Output.post-image {
  padding-left: 15px;
  padding-right: 23px;
  padding-bottom: round(22.5px, 15px + 10%);
}

`abs()`abs() permalink

Dart Sass: since 1.67.0
LibSass: ✗
Ruby Sass: ✗

LibSass, Ruby Sass, and versions of Dart Sass prior to 1.67.0 always parse abs() as a Sass function. To create a plain CSS calculation for those implementations, you can write something like abs(#{$number}) instead.

⚠️ Heads up!

The global abs() function compatibiliy with % unit parameters is deprecated. In the future, this will emit a CSS abs() function to be resolved by the browser.

The abs(value) takes in a single expressiona as a parameter and returns the absolute value of $value. If $value is negative, this returns -$value, and if $value is positive, it returns $value as-is.

  SCSS

  Sass

  CSS

  SCSS Syntax.post-image {
  // Since these abs() calls are valid calculation expressions, they're
  // parsed as calculations.
  padding-left: abs(10px);
  padding-right: math.abs(-7.5%);
  padding-top: abs(1 + 1px);
}

  Sass Syntax.post-image
  // Since these abs() calls are valid calculation expressions, they're
  // parsed as calculations.
  padding-left: abs(-10px)
  padding-right: math.abs(-7.5%)
  padding-top: abs(1 + 1px)


  CSS Output.post-image {
  padding-left: 10px;
  padding-right: 7.5%;
  padding-top: 2px;
}

Calculations

SCSS Syntax

Sass Syntax

💡 Fun fact:

SimplificationSimplification permalink

⚠️ Heads up!

SCSS Syntax

Sass Syntax

CSS Output

OperationsOperations permalink

SCSS Syntax

Sass Syntax

ConstantsConstants permalink

SCSS Syntax

Sass Syntax

SCSS Syntax

Sass Syntax

Calculation FunctionsCalculation Functions permalink

💡 Fun fact:

Legacy Global FunctionsLegacy Global Functions permalink

⚠️ Heads up!

min() and max()min() and max() permalink

SCSS Syntax

Sass Syntax

CSS Output

round()round() permalink

SCSS Syntax

Sass Syntax

CSS Output

abs()abs() permalink

⚠️ Heads up!

SCSS Syntax

Sass Syntax

CSS Output

`min()` and `max()`min() and max() permalink

`round()`round() permalink

`abs()`abs() permalink