sass-function to convert px to rem or em / extracted from the foundation-framework

rem-calc.scss

// This is the default html and body font-size for the base rem value.
$rem-base: 16px !default;

// STRIP UNIT
// It strips the unit of measure and returns it
@function strip-unit($num) {
  @return $num / ($num * 0 + 1);
}

// CONVERT TO REM
@function convert-to-rem($value, $base-value: $rem-base) {
  $value: strip-unit($value) / strip-unit($base-value) * 1rem;
  @if ($value == 0rem) { $value: 0; } // Turn 0rem into 0
  @return $value;
}

// REM CALC

// New Syntax, allows to optionally calculate on a different base value to counter compounding effect of rem's.
// Call with 1, 2, 3 or 4 parameters, 'px' is not required but supported:
//
//   rem-calc(10 20 30px 40);
//
// Space delimited, if you want to delimit using comma's, wrap it in another pair of brackets
//
//   rem-calc((10, 20, 30, 40px));
//
// Optionally call with a different base (eg: 8px) to calculate rem.
//
//   rem-calc(16px 32px 48px, 8px);
//
// If you require to comma separate your list
//
//   rem-calc((16px, 32px, 48), 8px);
//
// Example:
//
// font-size: rem-calc(24);

@function rem-calc($values, $base-value: $rem-base) {
  $max: length($values);

  @if $max == 1 { @return convert-to-rem(nth($values, 1), $base-value); }

  $remValues: ();
  @for $i from 1 through $max {
    $remValues: append($remValues, convert-to-rem(nth($values, $i), $base-value));
  }
  @return $remValues;
}


@function em-calc($values) {
  $remValues: rem-calc($values);

  $max: length($remValues);

  @if $max == 1 { @return strip-unit(nth($remValues, 1)) * 1em; }

  $emValues: ();
  @for $i from 1 through $max {
    $emValues: append($emValues, strip-unit(nth($remValues, $i)) * 1em);
  }
  @return $emValues;
}